Found one error in ftp.module (tested os4 version, but imho will be the same everywhere). To reproduce:
-- spawn adressbook.
-- create any new entry
-- press RMB, and choice "save". It will save a file called "ftp_sites" in the dopus5:System directory. All ok.
Again change anything in addressbook (add new entry, or edit previous one), and then again RMB and choice "save", and we have:
Directory Opus Request Error Saving File ! DOS error 205: object not found retry/chancel
Looks like some code didn't close normally file when save or something ?