Use the SEARCH=YES option on the checkin command.  Otherwise, it assumes that
the cartridge you're checking in is not yet in the library, and it looks for
an empty slot to store it in.  That's why you got the "library is full"
message,
there's no place to put VOL002 because all the cells are already full.

Actually, I can't explain how it was able to checkin VOL001;  you should have
gotten the same message then, too.

Craig Bell