301

Explanation
During processing of a WAIT macro, the system found
that the wait flag was already on in the event control block (ECB).
The flag on indicated that a previous WAIT macro was already waiting
for posting of the ECB.

System action
The system abnormally ends the program that issued
the WAIT macro.

System programmer response
  If the error recurs and the program
is not in error, look at the messages in the job log for more information.
Search problem reporting data bases for a fix for the problem. If
no fix exists, contact the IBM® Support
Center. Provide the program listing and the assembly listing associated
with the job.

Programmer response
Change the problem program to eliminate
a double wait on a single event. If no double wait is found, ensure
that the program did not incorrectly modify the ECB. Then run the
job again.

Source
Task management