I get this error when running my Moq tests through Teamcity 5
Test(s) failed. System.IO.FileNotFoundException : Could not load file or assembly \'
I had a similar issue, but found that I had different version's of Moq between my 2 Test projects.
The issue that I had was that the correct version was not available.
Just do
Update-Package Moq
From the Package Manager command line