The semaphore timeout period has expired (0x80070079))

I have DPM 2012 R2 with physical and virtual tape libraries, from last few days DPM is unable to write data on Physical Tape Library (Dell ML600). Every time a scheduled backup job runs or if i run it maually or if i try to erase the tape, below mentioned error is generated : 

The operation failed because of a protection agent failure. (ID 998 Details: The semaphore timeout period has expired (0x80070079))

Backup jobs on Virtual tape library are running fine, it's just the pysical tape library on which operations are getting failed. Any help regarding this will be higly appreciated !!