E03

Explanation
A task tried to end normally by issuing a RETURN
macro or by branching to the return address in register 14. The task
was not ready to end processing because the task issued one of the
following macros with a SET,MC (must complete) parameter: STATUS
RESERVE
ENQ

 The task did not issue an accompanying STATUS RESET,MC or DEQ
RESET,MC macro to reset the step-must-complete status before attempting
to end.

System action
The system abnormally ends the task.

Operator response
If the application or system programmer asks
for an SVC dump, set the following SLIP trap: SLIP SET,COMP=E03,ACTION=SVCD,END

System programmer response
  If the module is an IBM® module, search problem reporting data bases
for a fix for the problem. If no fix exists, contact the component
group for the module at the IBM Support
Center. Provide problem data collected.

Programmer response
Do the following: If a dump is not produced with the abend, ask the operator
to set a SLIP trap to obtain an SVC dump.
From the dump, identify the abnormally ended module.
If the module is an installation-provided program, ensure that
each ENQ, RESERVE, or STATUS macro with the SET,MC parameter is paired
with a DEQ or STATUS macro with the RESET,MC parameter.

Source
Recovery termination manager (RTM)