Resurrecting this one, because searching for "TapeBlockSize" turned up only this topic. My latest updated v9 (fresh install on Win2k12 both VBR and tape servers) occasionally throws a similar error (87, set parameters) w/ some tapes that do not match its set block size. Some bot not all. Recently while contacting support to help trouble shoot slow tape speed they added this registry key, and it's set to 800000 hex. I do not have the "setTapeMediaBlockSizeToDrive" entry though.
My drive properties in the GUI are set to 131072. Not sure how much of this matters, but it has been bugging me in the back of my head that I don't know what the above registry entry is doing.
Veeam B&R v9
Dell TL2000 via PE430 (SAS)