Summary

The application pooling feature in IIS 6 allows different web applications to run in the same process if they are part of the same application pool. However, it is not possible for applications that use different versions of ASP.NET to share the same process. If you attempt this type of configuration, you may receive the following error message in the Event log:

It is not possible to run different versions of ASP.NET in the same IIS process. Please use the IIS Administration Tool to reconfigure your server to run the application in a separate process.

Resolution

Make sure that each application pool only contains applications that use the same version of ASP.NET. Please see the following Microsoft Knowledge Base article for detailed information on assigning an application pool to an ASP.NET application and creating application pools.