Hi Charles...
This probably will not help...but here goes...
I had a similar problem several years ago, and what I found out was that if a tape media was written by another tape drive (which is not compatiable to your current drive) then this was a problem with BE recognising the foreign media. I understand that the 1st tape gets written too okay, but its any subsequent tapes that is the problem?
If you do an inventory on each tape ...is the label for each what you expect? If you perform a long erase on each, then relabel each, will the 2nd tape in a multiple volume backup work?
This sounds like a very tricky ones.
Cheers Roger