Troubleshooting Dynamics AX 2009 Enterprise Portal Unable to generate a temporary class

Recently, I bumped on this error while troubleshooting a webpart in AX 2009

Error

Server was unable to process request. ---> Unable to generate a temporary class (result=1).
error CS2001: Source file 'C:\WINDOWS\TEMP\vmeyu2da.0.cs' could not be found
error CS2008: No inputs specified

Solution:

Give the app pool iis account read/write permissions to c:\windows\temp folder