FIX: You may receive an InvalidCastException error in an ASP.NET-connected Web application


You may receive an InvalidCastException error in a Microsoft ASP.NET-connected Web application when the following conditions are true:
  • The Web application uses a master page, a user control, or pages that reference each other.
  • The master page, the user control, or the pages are batch compiled into a single assembly.
  • One of the batched dependencies is changed and causes a recompilation.
  • A dynamic call to load a reference is made, such as a call to the LoadControl method.
In this case, you may receive an error message that resembles the following:
Unable to cast object of type 'ASP.type' to type 'ASP.type'.
Note In this error message, type is a placeholder for one of the batch compiled types.

You may also receive an error message that resembles the following:
Could not load file or assembly 'App_Web_xxxxxxxx, Version=, Culture=neutral, PublicKeyToken=null' or one of its dependencies. The system cannot find the file specified.


A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

To download this hotfix from the MSDN Code Gallery, visit the following Microsoft Web site:

Note The MSDN Code Gallery displays the languages for which the hotfix is available. If you do not see your language listed, it is because the Code Gallery resource page is not available for that language.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site:

The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.
File nameFile versionFile sizeDateTime


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

More Information

For more information, click the following article numbers to view the articles in the Microsoft Knowledge Base:

824684 Description of the standard terminology that is used to describe Microsoft software updates

919284 Error messages when you try to run an ASP.NET 2.0 Web application that is built on the .NET Framework 2.0

934839 FIX: You may receive an exception when you browse a .NET Framework 2.0 ASP.NET Web application