Hi Sebastian -
The most likely cause of this problem is that the tests are making assumptions about the locations of DLLs that they are depending on. Normal (non-NCrunch) test runners will generally run tests within a directory that contains all the DLLs that are to be loaded into the test runner application domain, though NCrunch will instead wire together an application domain dynamically in order to improve build performance.
There are a number of ways you can solve this problem. Have a look at the 'Assumptions About Referenced Assemblies Locations' section of the troubleshooting tests guide in the wiki -
https://www.ncrunch.net/...-runtime-related-issues
Cheers,
Remco