You receive an ASP.NET error in your Event Viewer while using IIS 6.0 on your server:
“It is not possible to run two 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.”
IIS 6.0 uses the process w3wp.exe. One or more application can run together in one ore more processes within the same application pool by ‘application pooling’, an isolation feature of IIS. Each pool has it’s own worker processes which handles requests. When you are using multiple versions of ASP.NET on your server, these processes will conflict with each other if using the same application pool. Therefore each ASP.NET version has to use it’s own application pool.