Web Debug

Fix broken web applications, from servers to clients.

Troubleshoot IE memory leak

Understanding and Solving Internet Explorer Leak Patterns

The following sections will discuss patterns of memory leaks and point out some common examples of each pattern. One great example of a pattern is the closure feature of JScript, while another example is the use of closures in hooking events. If you're familiar with the event hooking example, you might be able to find and fix many of your memory leaks, but other closure-related issues might go unnoticed.
Now, let's look at the following patterns:

Troubleshoot heap corruptions

Detecting Heap Corruption Using GFlags and Dumps
By Dan's WebDAV 101

One way to check for heap corruption is using gflags.exe in combination with a debugger (you can use ADPlus which will attach a debugger for you) to take a dump. This checking is not a 100% catch-all, however it works fairly well. Using gflags to do this type of check will cause an application (as an example the w3wp.exe for the worker process under IIS for a web application) to crash when there is heap corruption. When a debugger (such as what ADPlus would use) is to the process and there is a detected corruption, a crash dump will be created which can be used to find which module (dll, etc) caused the corruption. There was a similar program in the past called pageheap.exe; however, its functionality has been merged into gflags.exe.

Troubleshoot Form Authentication Issue

Troubleshooting Forms Authentication

Published on April 9, 2012 by Apurva Joshi

Often, while using Forms Authentication in an ASP.NET web application; there is a need to troubleshoot a problem that occurs when a fresh or an ongoing request is intermittently redirected to the application’s login page. You can easily debug this problem on Visual Studio IDE by attaching a debugger in a development environment. In production environments, however, the task becomes hectic and problematic. To troubleshoot a random problem like this one, you need to log information related to the problem so that you can narrow down the root cause.

In this troubleshooter guide, we'll briefly cover the Forms Authentication concept. We'll then look into which scenarios lead to a user being redirected to the login page and how to capture data that is relevant to isolating the problem. We'll also cover how to implement an IHttpModule interface to log the Forms Authentication information.

Troubleshoot IIS 500 errors

IIS 6

  • 500 - Internal server error. You see this error message for many server-side errors. Your event viewer logs may contain more information about why this error occurs. Additionally, you can disable friendly HTTP error messages to receive a detailed description of the error. For more information about how to disable friendly HTTP error messages, click the following article number to view the article in the Microsoft Knowledge Base:
    294807 HOW TO: Disable Internet Explorer 5 'Show Friendly HTTP Error Messages' Feature on the Server Side
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  • 500.12 - Application restarting. This indicates that you tried to load an ASP page while IIS was restarting the application. This message should disappear when you refresh the page. If you refresh the page and the message appears again, it may be caused by antivirus software that is scanning your Global.asa file. For additional information, click the article number below to view the article in the Microsoft Knowledge Base:
    248013 Err Msg: HTTP Error 500-12 Application Restarting
  • 500-100.ASP - ASP error. You receive this error message when you try to load an ASP page that has errors in the code. To obtain more specific information about the error, disable friendly HTTP error messages. By default, this error is only enabled on the default Web site. For more information about how to see this error on non-default Web sites, click the following article number to view the article in the Microsoft Knowledge Base:
    261200 HTTP 500 error message displays instead of ASP error message from 500-100.asp


IIS 7, IIS 7.5, IIS 8










500 Internal server error. This HTTP status code may occur for many server-side reasons. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

942031 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 500.0 - Internal Server Error"
500.11 Application is shutting down on the web server. The request is not processed because the destination application pool is shutting down. Wait for the worker process to finish shutting down, and then try the request again. If this problem persists, the web application may be experiencing problems that prevent the web application from shutting down correctly.
500.12 Application is busy restarting on the web server. The request is not processed because the destination application pool is restarting. This HTTP status code should disappear when you refresh the page. If this HTTP status code appears again after you refresh the page, the problem may be caused by antivirus software that is scanning the Global.asa file. If this problem persists, the web application may be experiencing problems that prevent the web application from restarting correctly.
500.13 Web server is too busy. The request is not processed because the server is too busy to accept any new incoming requests. Typically, this HTTP status code means that the number of incoming concurrent requests exceeds the number that the IIS 7.0, IIS 7.5, or IIS 8.0 web application can process. This problem may occur because the performance configuration settings are set too low, the hardware is insufficient, or a bottleneck occurs in the IIS 7.0, IIS 7.5, or IIS 8.0 web application. A common troubleshooting method is to generate a memory dump file of the IIS 7.0, IIS 7.5, or IIS 8.0 processes when the error is occurring and then to debug the memory dump file.
500.15 Direct requests for Global.asax are not allowed. A direct request for the Global.asa file or for the Global.asax file is made. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

942030 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 500.15 - Direct request for global.asa are not allowed"
500.19 Configuration data is invalid. This HTTP status code occurs because of a problem in the associated Applicationhost.config file or in the associated Web.config file. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

942055 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 500.19 - Internal Server Error"
500.100 Internal ASP error. An error occurs during the processing of an Active Server Pages (ASP) page. To obtain more specific information about the error, disable friendly HTTP error messages in the web browser. Additionally, the IIS log may show an ASP error number that corresponds to the error that occurs. For more information about ASP error messages and about the meaning of ASP error messages, click the following article number to view the article in the Microsoft Knowledge Base:

294271ASP error codes

Troubleshoot IIS 404 errors

IIS 6

404 - Not found. This error may occur if the file that you are trying to access has been moved or deleted. It can also occur if you try to access a file that has a restricted file name extension after you install the URLScan tool. You will see “Rejected by URLScan" in the w3svc log files after you install the URLScan tool. In this case, you see "Rejected by URLScan" in the log file entry for that request. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

248033 How system administrators can troubleshoot an "HTTP 404 - File not found" error message on a server that is running IIS

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  • 404.1 – Web Site not accessible on the requested port. This error indicates that the Web site you are trying to access has an IP address that does not accept requests for the port on which this request came. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
    248034 IIS Error: 404.1 Web Site Not Found
  • 404.2 – Lockdown policy prevents this request. In IIS 6.0, this indicates that the request has been prohibited in the Web Service Extensions list. For more information, click the following article numbers to view the articles in the Microsoft Knowledge Base:
    328419 How to add and remove Web Service Extension files in IIS 6

    328505 How to list Web Server Extensions and Extension files in IIS 6.0

    328360 How to enable and disable ISAPI extensions and CGI applications in IIS 6.0
  • 404.3 - MIME Map policy prevents this request. This problem occurs if the following conditions are true:
    1. The handler mapping for the requested file name extension is not configured.
    2. The appropriate MIME type is not configured for the Web site or for the application.



IIS 7, IIS 7.5, IIS 8



















404.0 Not found. The file that you are trying to access was moved or does not exist. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

942041 Error message when you try to open a webpage that is hosted on IIS 7.0: "HTTP Error 404.0 - Not Found"
404.2 ISAPI or CGI restriction. The requested ISAPI resource or the requested CGI resource is restricted on the computer. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

942040 Error message when you try to visit a webpage that is hosted on a computer that is running IIS 7.0: "HTTP Error 404.2 – Not Found"
404.3 MIME type restriction. The current MIME mapping for the requested extension type is not valid or is not configured. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

942032 Error message when users visit a website that is hosted on a server that is running Internet Information Services 7.0: "HTTP Error 404.3 - Not Found"
404.4 No handler configured. The file name extension of the requested URL does not have a handler that is configured to process the request on the Web server. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

942052 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 404.4 - Not Found"
404.5 Denied by request filtering configuration. The requested URL contains a character sequence that is blocked by the server. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

942053 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 404.5 - URL Sequence Denied"
404.6 Verb denied. The request is made by using an HTTP verb that is not configured or that is not valid. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

942046 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 404.6 - VERBDENIED"
404.7 File extension denied. The requested file name extension is not allowed. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

942045 Error message when you try to browse a webpage that is hosted on IIS 7.0: "HTTP Error 404.7 - FILEEXTENSIONDENIED"
404.8 Hidden namespace. The requested URL is denied because the directory is hidden. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

942047 Error message when you try to visit a webpage that is hosted on IIS 7.0: "HTTP Error 404.8 - HIDDENNAMESPACE"
404.9 File attribute hidden. The requested file is hidden. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

942049 Error message when you try to visit a website that is hosted on IIS 7.0: "HTTP Error 404.9 - File Attribute Hidden"
404.10 Request header too long. The request is denied because the request headers are too long. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

942077 Error message when you visit a website that is hosted on a server that is running Internet Information Services 7.0: "HTTP Error 404.10 - REQUESTHEADERTOOLONG"
404.11 Request contains double escape sequence. The request contains a double escape sequence. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

942076 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 404.11 - URLDOUBLEESCAPED"
404.12 Request contains high-bit characters. The request contains high-bit characters, and the server is configured not to allow high-bit characters. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

942075 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 404.12 - URLHASHIGHBITCHARS"
404.13 Content length too large. The request contains a Content-Length header. The value of the Content-Length header is larger than the limit that is allowed for the server. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

942074 Error message when you visit a website that is hosted on a server that is running Internet Information Services 7.0: "HTTP Error 404.13 - CONTENTLENGTHTOOLARGE"
404.14 Request URL too long. The requested URL exceeds the limit that is allowed for the server. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

942073 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 404.14 - URLTOOLONG"
404.15 Query string too long. The request contains a query string that is longer than the limit that is allowed for the server. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

942071 Error message when you visit a website that is hosted on a server that is running IIS 7.0: "HTTP Error 404.15 - Not Found"
404.17 Dynamic content mapped to the static file handler. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

2019689 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 404.17 - Not Found"

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