Per the folks at Microsoft PSS, there's a rollup package for VSS at http://support.microsoft.com/kb/940349. This is a hotfix, so note that regression testing is not complete and you should proceed with caution. You'll need to reboot after installing this package.
After the reboot, you'll need to re-register VSS's corresponding DLLs. Enter each line in a command window and press enter after each.
cd /d %windir%\system32
net stop vss
net stop swprv
regsvr32 /i swprv.dll
regsvr32 /i eventcls.dll
(the last entry may not run successfully)
Reboot the server again.
This procedure may not be applicable to your situation, so back up your system before proceeding.