You may encounter tapes in Microsoft Data Protection Manager libraries that're written with an unsupported block size and first need to be erased because DPM cann't evaluate such tapes and therefore willn't do anything to it. The ZIP file linked below contains a script, script user guide and two utilities to accomplish this on a DPM server that controls a library. The utilities actually are testing tools that provide the necessary functions to control changers and tape drives. The script automates the various steps and simplifies the syntax for erasing tapes: Usage: DPMeraseTape.Ps1 <slot number> <unique part of library friendly name>.
The script will load media from <slot number> into an empty tape-drive, erase the tape and move media back into the slot again.
Download: Script & User Guide