That is not a VMware Fusion error per se, it's a Windows error message so act accordingly. Meaning it's irrelevant that you're running Windows in a Virtual Machine and diagnosing/troubleshooting is essentially no different the when running in a Physical Machine. So with the lack of information you've provided I'd suggest you Google or search Microsoft, otherwise...
To help figure out what is what, the best way to provide comprehensive diagnostic information is to use the "Collect Support Information" command from the VMware Fusion (menu bar) > Help > Collect Support Information and then attach the .tgz file it created on your Desktop to a reply post.
Note: Use the "Use advanced editor" link in the upper right corner of the normal reply window to bring up the Advanced Editor where you'll be able to attach files via the Choose File button or Browse button (depending on the Browser) above the Post Message button!