When attempting a Windows System (volume) backup, you may get the error: the error "The location for backup is a critical volume" which is flagged by WBAdmin. This means the temporary storage drive that you have specified is actually a critical volume. This is a restriction impose by Microsoft's WBAdmin that the backup location of a System Backup cannot be on a critical volume.
Microsoft has provided a workaround. You can actually enable System State backup to critical volumes by following the steps in the following Microsoft document: http://support.microsoft.com/kb/944530/en-us