Corrupted 64 bit IIS 7 with 32 bit .Net 1.x; how to fix/reset

If you get the following with IIS:

ISAPI Filter 'C:\Windows\Microsoft.NET\Framework\v4.0.30319\aspnet_filter.dll' could not be loaded due to a configuration problem. The current configuration only supports loading images built for a AMD64 processor architecture. The data field contains the error number. C1000000

There is a problem with the application pool, go in to IIS manager and then select the application pool advanced setting.

The application pool must have 32 bit application option enabled.