When trying to enter a tape into an IBM ATL or VTS,the CBRUXENT exit may reject the entry and indicate that the tape is a foreign tape. The TMC is correctly updated even though the tape is rejected.
Check your SYSLOG for the message IEFTMS9 BACKUP REQUIRED, AUDIT FILE UTILIZATION IS CURRENTLY xx%. If the audit file has reached the threshold that you set in the options for CA 1 (THAUDT) then CBRUXENT will treat the insert as a foreign tape. Run TMSCOPY and then retry the entry of the tape.