Unit Test Runner failed to run tests - CodedUITestFramework

Hello,

I'm trying to upgrade a solution from VS2010 to VS2013.

I have ReSharper 8.0.2 (8.0.2000.2660) C# edition.  In VS2010 both NUnit unit tests and Spec Flows run just fine.

If I open using VS2013, rebuild, attempt to run tests NUnit unit tests work fine but Spec Flows generate the message:

Unit Test Runner failed to run tests

System.IO.FileNotFoundException

Trying to load "Microsoft.VisualStudio.QualityTools.CodedUITestFramework"  Version=12.0.0.0, etc...

The file exists and the reference in the project is correct.

Any ideas?