I came here searching for the solution for a similar problem. Posting this answer just in case the solution I found helps someone else.
This solved it for me in Visual Studio (2012):
Add New Item -> Test Settings 
Change the testsetting 
By default this is set to “Force test to run in 32 bit process”
From the menu:
Test -> Test Settings -> Select Test Settings File -> Choose the test settings file you have created.
Now run the tests.