I have experienced different cases when nCrunch don't successfully detect unit test .
In the example below I made an "get latest" from source control. Then i received build errors from ncrunch. After manually compiled whole solution without error. And right click assemblies in ncrunch test list for reload. The build errors resolves. But UI in VS is not showing unit tests as tests any more.
http://imgur.com/AyAXFQe
Also the processing queue is empty.
I also submitted and bug report. So you get more VS information.