I just finished fixing this on one server I migrated. The VMWare converter leaves some residual traces of the Virtual Server additions on the converted machine. The mouse filter driver from Virtual Server seems to cause this. To get rid of it, there are two commands you'll need to enter on the server.
reg add HKLM\SYSTEM\CurrentControlSet\Control\Class\{4D36E96F-E325-11CE-BFC1-08002BE10318} /y /v UpperFilters /t REG_MULTI_SZ /d mouclass
sc delete msvmmouf
Usual disclaimers apply. This works for me, but I won't be held responsible if your virtualized server is engulfed in virtualized flames as a result of doing this. Make sure you have a complete backup, and so forth.
You probably don't need the sc command, but I didn't bother to find out if the msvmmouf service would re-register as a mouse filter as it started or not.
Other services left behind by the VMWare converter include msvmscsi (storage controller) and mrxvpc ("shared folders" redirector). They don't seem to cause any problems. I'd probably disable or delete the shared folders redirector anyway, though.