Parallels 6 fails with "virtual machine permissions" error

When I try to start Windows XP Pro on my Parallels 6 virtual machine, I get the error "Unable to change the virtual machine permissions. Parallels Desktop cannot set the required permissions or one or more objects in the virtual machine folder." Parallels Desktop does not, of course, provide any details on the specific permissions, nor the specific objects. Running Parallels Desktop 6 for Mac, build 6.0.11992, under Mac OS X, version 10.6.6.

The only previous hints I can find about this are for much earlier versions of Parallels.
Help!

 

Well, this doesn't give me a whole lot of confidence in the Forums, but it did take quite a while for my question to be posted on the forum. Actually, that delay does make it seem like the forums would be a poor choice for time-critical issues.

I repaired the permissions on my internal hard drive where Parallels is in the Applications folder. The option was not available on the external drive where I have my virtual drive located. I rebooted several times. Parallels now works, although it came up running in Windows mode rather than full screen mode.

Is there anyone out there with an idea of what happened?