Another stab... (feels like pinching kitties in the dark)
Do you share files between host and guest? If so, what happens if you disable that?
Really the best way to get help here is to provide technical details in the form of the support bundle or the vmware.log file of your trouble VM if you'd rather share less information. You can create the support bundle by selecting it from the Fusion help file and then attach the .tgz file it puts on the desktop to your reply here.
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Wil