The FairCom RTG BTRV interface returned 81 instead of 84 when attempting to read a locked record. As a consequence RM/COBOL programs returned error code 3081 instead of 9900 when attempting to read a locked record.
The FairCom RTG BTRV interface has been fixed to return the proper error code, which also solves the symptom seen in RM/COBOL.