Who knows? The U4043 Language Environment message says:
Explanation: Language Environment detected an unrecoverable error running a COBOL program. Before this abend is issued, Language Environment writes an IGZ message to the message file with the details of the error condition.
Programmer Response: Read the IGZ message in the Language Environment message file to determine the error.
Since you didn't provide the IGZ message, there's no way for us to tell.