If you are doing any multi-threading and are using MSTest, you will probably run across this error. For some reason, MSTest by default runs in STA threading mode. WTF, Microsoft! Why so stuck in the old COM world? When I run the same test using NUnit, I don't have this problem. Unfortunately, my company has chosen MSTest, so I have a lot of testing problems. NUnit is so much better, IMO. After determining that I wasn't referencing any unmanaged code that would flip the thread into STA, which can ......