Thanks for reporting this problem. I've tested the scenario you describe and I cannot reproduce it locally. Do you have this problem specifically with your project or with any NUnit (i.e. some simple "Hello world") test project as well?
If it only happens for your project then it's probably something specific in the project that causes this failure. You can try the following as a possible workaround:
1. Switch off the "Shadow-copy assemblies being tested
" option in JustCode | Options | Unit Testing.
2. Set the Copy Local setting of the NUnit assembly references in your test project to false.
3. Clean your test project's bin folder (delete everthing).
4. Rebuild and try to run the tests then.
If this does not help then we'll need some more details to try and pin-down the problem. It will be great if you can open up a support ticket and send us your Unit tests project.
the Telerik team