We had the same problem on Windows 2003 SP1 servers (with NetBackup 5.1MP3A to 5.1MP6) and a wide
range of hardware types.
In our cases, the Windows 2003 SP2 solved the problem.
Due to this error, we also had partially or completely emtpy C:\WINDOWS\system32 - directories !
We suppose, that the problem was caused by a certain nLite / scsi storeport installation configuration.
We also found a work around for Windows 2003 SP1 servers. However, the WINDOWS admin is right now on
holiday and he only knows the details regarding the work around....