Fix: IE Closes When Debugging a Windows Forms Control in Visual Studio .NET 2003

After my development team at work switched to developing using Visual Studio 2005 and the 2.0 .NET Framework, we encountered a problem trying to debug older versions of our Windows Forms controls running embedded in web pages viewed with Internet Explorer with Visual 2003. We would open our project or solution in Visual Studio 2003 and start the debugger to launch Internet Explorer, but shortly after the page with the Windows Forms control would start loading, Internet Explorer would just close with no error message, and the debugging session would end.

Another symptom of the same problem occurred when we instead would try to first open an Internet Explorer window normally and navigate to the web page containing our Windows Forms control, which would load correctly. Then, when trying to attach Visual Studio 2003 to the iexplore.exe process for debugging, Visual Studio would just fail with the error message "Unable to attach to the process."

We eventually determined that the problem was because Visual Studio 2005 along with the 2.0 .NET framework was installed on the development machine, Internet Explorer would load the Windows Forms control using the 2.0 framework (instead of the 1.1 framework as it had previously). Then, when Visual Studio 2003 (which uses the 1.1 .NET framework) tried to attach to the managed code in the iexplore.exe instance for debugging, it would (apparently) get confused and just fail.

The solution we came up with was to use a special iexplore.exe.config file to force IE to load controls using the 1.1 version of the .NET framework. To use this solution, open up a new text editor window and paste in the following text:

<configuration>
  <startup>
    <requiredRuntime version="v1.1.4322"/>
    <supportedRuntime version="v1.1.4322"/> 
  </startup> 
</configuration>

Then, save the file as "iexplore.exe.config" in your Internet Explorer folder (typically C:\Program Files\Internet Explorer). Finally, close and reopen any open Internet Explorer windows.

This will force Internet Explorer to use the version of the .NET framework specified in the file (in this case, 1.1.4322, the version number of the commercial release of the 1.1 framework) for any Windows Forms controls it loads.

To have IE revert to the original behavior of using the default version of the framework to load Windows Forms controls, just delete or rename the iexplore.exe.config file. (On my dev machine, I leave a copy of the file in my IE folder named "iexplore.exe.config_forcev11" for easy access when I need it.)