Registry errors

out of about 300 machines we have about 15 that come back with an error vnetsup registry needs to be restored. All 300 of these machines have basicly the same hardware. If the we restore system.dat with a backup we made when the machine was runningit will usually run 2 or 3 days and blow up again. Formating and starting form stratch doesn’t always help. After installing 98 the vnetsup error went away but we still get a registry corupt message and 98 tries to restore it. “Windows networking could not setup instance data error 6107 VNETSUP please reinstall windows.”
any help would be appreciated!