MsBuild cannot load NHibernate on TFS

Hi I have a set of MsTest tests that runs with NHibernate, SQLLite.I can succesfully load the assemblies from any DEV machine and run the tests.On TFS we have a drop folder where we put all the assemblies and a copy of MsTest.exe, where we run the unit tests from.The problem I get on TFS is the following:

Unit Test Adapter threw exception: Type is not resolved for member 'NHibernate.HibernateException,NHibernate, Version=3.3.1.4000, Culture=neutral, PublicKeyToken=aa95f207798dfdb4'..

But this assembly and the related dependencies are copied to the drop location, so I don't understand why MsTest can't load this assembly. I run the tests using this command in MsBuild:

mstest /testcontainer:"mydll.dll" /detail:errormessage /detail:errorstacktrace

But unfortunately I can't see the real error, I guess it is related to SQLLite.