So you've got a multi-volume backup, the first volume of which no longer exists, and you want to release the second volume, unusable for anything at the moment, to scratch?
I'd go with Steve Myers' suggestion. It seems that the only thing CA1 knows about it that is stopping it being processed to scratch is that it is in a "vault".
It doesn't look like a tape which is "cataloged" as such, just a volume which is recorded as being in a vault, and which can't be reused until it is booked out of there.
If that works, ensure that procedures for dealing with damaged tapes take into account subsequent volumes where they exist.
If that fails, how about treating it is a "damaged" tape?