When running Copycat to copy multiple files from one tape to another, the allocation for the second input file is not being handled correctly. You may receive the CTC7305A message (CTC7305A Unit currently in use - xxx) followed by the CTC7303R message (CTC7303R Reply 'retry', 'wait', 'abend', or 'bypass').
Check your ACS routines and make sure that Copycat is allowed to request a specific drive during allocation. If the allocation is passed to another product such as VAM the actual allocation may go to another device causing this type of problem.