I am having the same trouble.
I upgraded to Isolator 4.2.3 last week. When I did TDD.NET stopped working so I upgraded that as well. I'm now trying to run my NUnit (22.214.171.124) tests using TDD.NET (2.12.2179) and TI (4.2.3).
I get the following error:
failed: TypeMock.TypeMockException :
*** Typemock Isolator needs to be linked with Coverage Tool to run, to enable do one of the following:
1. link the Coverage tool through the Typemock Isolator Configuration
2. run tests via TMockRunner.exe -link
3. use TypeMockStart tasks for MSBuild or NAnt with Link
For more information consult the documentation (see Code Coverage with Typemock Isolator topic)
at TypeMock.MockManager.Init(Boolean collectAllCalls)
If I uninstall and reinstall TI then it goes away for awhile but then comes back. I also run tests from the command-line via MSBuild. Those scripts register TypeMock.
Furthermore, if I try to run my unit tests in the debugger I get another error when MockManager.Init() is called. It indicates that it failed to load "c:\winnt\system32\tmService.dll".