Found that the fast inventory of the Tape library in DPM can fail or show the wrong results in some cases. According to a newsgroup post this can be caused (in certain types of libraries) by the press of a cleaning tape.
The post reports this for IBM 35XX series and HP 1/8 tape libraries. We have seen the same issue on the Dell TL2000 tape library which is actually an IBM Totalstorage 3573 Tape library.
The workaround is to remove the cleaning tape from the library.
The newsgroup threat also describes a fix setting a registry key. (I have not tried this yet)
The rekey fix is to handle some unexpected behavior of tape library. The issue is when there is cleaner media present in some library element (slot/drive/transport ) the IOCTL_CHANGER_GET_ELEMENT_STATUS for that particular elment returns with ELEMENT_STATUS_EXCEPT set in CHANGER_ELEMENT_STATUS.Flags and CHANGER_ELEMENT_STATUS.ExceptionCode is set to ERROR_UNHANDLED_ERROR. This is unexpected behavior as per WHQL and as a result of this you will see Fast Inventory failing with "Hardware Issue". The workaround is added in DPM 2007 SP1 and we have seen this issue with only IBM 35XX series and HP 1/8 tape library
Thanks to Sachin