A03

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 either: The task had attached one or more subtasks that had not ended.
The task did not detach a subtask that it had previously attached
with the event control block (ECB) option.

System action
The system abends the task.

Operator response
If the system or application programmer asks
for an SVC dump, set the following SLIP trap: SLIP SET,COMP=A03,ACTION=SVCD,END

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

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
from the contents directory entry (CDE) or from the PRBRSV field in
the associated RB.
If the module is an installation-provided program, change the
program so that, before the task ends, all its subtasks will end.
 A task can determine that its subtasks have ended by specifying event
control block (ECB) operands in ATTACH macros that initiate the subtasks,
and then issuing WAIT macros that specify ECBs representing the end
of its subtasks. When the ECB option has been specified with the
ATTACH macro, the task must detach its subtask once notification of
subtask ending has been received. Failure to do so will result in
this abend.
 If a WAIT macro had been issued and the ECBs indicated
that all subtasks had ended, check for program errors that incorrectly
modified the WAIT macros or ECBs.
 After making corrections,
recompile the program. Run the job step again.

Source
Recovery termination manager (RTM)