I am running Microsoft Exchange 2003 SP2 on a Windows Server 2003 R2 SP2. I am using NTbackup to backup Exchange to my File Server (Win 2003 Srv) where I have a Tape Drive attached. I backup the exchange server to a mapped drive on the file server where a backup is performed later that night. When running my fullbackup, sometimes the backup is successful and sometimes its not. When the back fails I get :Error: MyServer\Microsoft Information Store\First Storage Group is not a valid drive, or you do not have access. I googled this error and checked all the solutions provided and everything in my environment checks out. Microsoft admitted a bug in Ntbackup but this was supposed to have been fixed in SP1 of Server 2003. I recommended a switch to Backup Exec 11d but it got shot down due to money problems. Has anyone run into this problem before and if so, how did you resolve the issue.