Hi Sergo,
Thanks for sharing this problem.
The main issue here is that with the test class descending from a UserControl, the code within the UserControl class (probably the constructor) is being executed during test discovery. I'm not sure what exactly happens inside this code, but it probably would vary depending on your platform.
You may be able to work around this problem by setting the 'Framework utilisation type for NUnit' solution-level configuration setting to 'StaticAnalysis'. This will turn off the dynamic test discovery step, causing NCrunch to statically detect the tests instead. It's quite probable that you'll then receive a similar error downstream when NCrunch later constructs the fixture in order to execute its tests.
NCrunch was never designed to work with tests that descend from a complex type such as UserControl. Tests are expected to be simple classes containing code that you are able to easily change and understand. I'm afraid that a technical fix for this issue from the side of NCrunch isn't possible to provide. If the Framework utilisation type setting doesn't allow the test to execute, you'll need to redesign the fixture.
You may also want to have a look at the
troubleshooting section under 'System.Security.VerificationException: Operation could destabilize the runtime'. This category of failure is similar to the error you're experiencing .. it's possible that the solutions suggested may be applicable in your case.