Unit Test Adapter threw exception: Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information

I have a windows application containing certain unit tests, whenever i try to run or debug any unit test i get the below error in test explorer-

Unit Test Adapter threw exception: Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information..

I'm using Visual studio 2012 premium with the latest update and Code coverage is not enabled. Any help in resolving the issue is highly appreciated.