All of a sudden after weeks of successful tape backups they are now failing because SBS2003 tries to install drives for "Generic volume shadow copy". Each time volume shadow copy is activated either by ntbackup or by the shared folder volume shadow copies, SBS pops up the found new hardware balloon and tries to install drivers for "Generic volume shadow copy". It then shows the dialog box that the driver has not passed Windows logo testing and asks if I want to proceed. If I'm at the console and allow it to continue, the backup will work fine. Of course this is not normally the case so the backups via volume shadow copy fail.
Try renaming C:\Windows\system32\CatRoot2 to C:\Windows\system32\CatRoot2.sav and reboot the system.