InvalidProgramException

I have about 200 unit tests that pass when run with MbUnit.Cons.exe however they fail when run at the command line with NCover 1.5.4beta and MbUnit 2.3.0.0, all with InvalidProgramException like so:

Test: DurationTypeFixture.DurationFactory.MatcherExactly.TestGetSchema Type: Failure Message: Common Language Runtime detected an invalid program.

   at Com.Ccur.Vod.Common.Schemas.Repository.Tests.BaseValueTypeFixture`1.TestGetSchema(T cm)

They actually all pass when run with TestDriven.NET in VisualStudio.NET 2005 with the same versions of MbUnit and NCover. All the tests are related to generics, but there don't seem to be any yields in site.

Weird I know, what might I be doing wrong?. I can provide any necessary information.

Thanks in advance.