I am getting this too, I can't copy from XP to OS X. Clipboard Synchronization is enabled, but nothing happens in OS X.
And I still get the Tools installation running, even though I've tried dozens of times to disable the Tools CD image. Still comes up every time I restart the VM.
Restarting Windows works here. I have to do this at least every couple of days. I've had the issue since at least #4124 but I think I've had it on #3188 as well.
I'm still looking for an fix that doesn't require me to close Outlook. I hate waiting for Outlook to do its thing. Oh for a native app that talks Exchange properly, but that's another issue entirely.
Edit: Okay, I tried restarting the Parallels services and logging off/on Windows to no avail. Then I discovered mpemburn's tip which did the trick.