TMockRunner won't run??

Hello all, I'm enjoying TypeMock - but ran into a strange issue. I used the "TMockRunner.exe" to launch the NUnit gui to run some tests last night - and everything worked fine. Today, I try again, and I get this error:

C:Program FilesTypeMockTypeMock.NETTMockRunner.exe is not a valid Win32 application

After I click "OK" an additional message is displayed in the command window: "Access is denied"

Here's how I'm calling it with the command line:

C:Program FilesTypeMockTypeMock.NET>TMockRunner.exe "c:Program FilesNUnit 2.4in unit.exe"

Again, this has worked for me once - but that's it. I've confirmed that TypeMock is enabled (using the "Tools" menu in VS).

Any ideas? Thanks in advance.
Chad