I have had a problem running under multiple processors. Set your processor usage to a single processor. This was an issue some tima ago, and I don't think it has really been addressed sufficiently. I have about 35 to 40 Parallels installations around my network, and I set them all to a single processor for this very same reason. It helped tremendously.
Don't bother talking to support about it, I went through a long series of conversations with them via email, and they won't even admit there might be a problem here, although I think they know there is.