>...Is there a special
>procedure for checking in a cleaner cartridge?

No: you simply toss them into the Convenience I/O station and the
library puts them away into arbitrary cells, remembering where
they are.  I would hazard that the tape you inserted did not have
a barcode label prefix matching the one you originally selected
at the library's control panel.

I concidentally added a few cleaning tapes to my library this
morning, and they are all recognized, having our chosen "CLN" prefix.

  Richard Sims, BU