This is likely to be related to NCrunch's handling of the .deps file used to build the test environment.
This issue is probably the same one. You'll find a published build in this thread that will likely solve this problem.
I'm hoping to release v3.10 this week, which will include the above fix and will likely solve dependency inconsistencies.
Note that you'll need to have the 'Copy referenced assemblies to workspace' setting turn on for all projects in your solution if you want the above fix to work correctly.