When i tried running an ibattis related unit test fixtures in my exsiting test assembly I started getting this wierd error that's a known bug documented at http://support.microsoft.com/kb/327131.
Interesting thing is that when i run that fixture in a separate assembly it works fine but as soon as i add it to existing test fixtures it crashes with this error :"The invoked member is not supported in a dynamic assembly".
I think it has to do with how nUnit created dynamic assemblies for test fixtures internally. Unfortunately i cant change that behavior. So for now the work around is to use a separate assembly.