We are running a single Exchange 2007 server and just replaced backup exec 11d with DPM 2007. I am using the Microsoft recommended "Firestreamer" product to allow quasi tape backups to local disk. Backups are currently failing with error details: "Failed to perform the operation since the free tape is not available in Stand Alone Drive Tape Library Firestreamer Drive - ID 24050"
Having said that, I am using the same backup destination for file server backups through DPM and those jobs complete perfectly. Space is not an issue as the current firestreamer 'image' is hovering right around 14 GB on a drive with 300GB + of capacity. Not sure why this is only happening with exchange jobs?