Just started happening today for me...
iMac, 2GB RAM (1GB alotted to Parallels), 2.16 GHz Intel Core 2 Duo, Tiger (10.4.10). Win XP on VM.
Something about last night could have contributed: I normally logout in the evening, however, my logout hung on an application (though Parallels appears to have suspended long before that application requested action).
I came in this morning, restarted Parallels, was greeted by the hung VM message, but... as I compose this message, the VM has resumed! So it appears to be something about the clean up from the previous suspension call.
HTH the techs. I'm going to shutdown and restart the VM, suspend and resume to clean up any stale *.sav files.
Tim