I have the same issue
I just started getting this yesterday.
Running under OS X 10.6.4, Windows 7 Home Premium with 2GB allocated, Parallels 6.0.11828 on MBP 15" 8GB.
I have not yet upgraded to OS X 10.6.5. I upgraded to Parallels 11828 a week or so ago, but have been using the VM since that time (up until yesterday) in coherence mode.
In a related post, it was recommended to reinstall Parallels Tools. I did this, but still can't get Win7 to change to coherence.
I have a second VM guest running Windows XP -- coherence works fine on that instance.
Last edited: Nov 11, 2010