Check the contents of the REAS= of the message. In the above sample you will see that REAS= as a hex 'XXXX0012' Unix Reason Code.
Search for the meaning of the Unix Reason Code in this IBM document: IBM Knowledge Center
Reason Code x'0012' indicates:
JRMaxChild
The maximum number of processes for this user ID has been exceeded.
Action: Ask the system programmer or system administrator to increase the MAXPROCUSER
parameter of the BPXPRMxx parmlib member.
Have your Systems Programmer and/or your Security Administrator verify:
a. If the value for MAXPROCUSER needs to be increased in the BPXPRMxx parmlib.
b. If the userid in question has its own OMVS segment. If the userid does not have
its own OMVS segment, it may be defaulting to a default OMVS segment that has a
low value for PROCUSER. You will need to increase the value or define a OMVS
segment for that particular userid with the proper value for PROCUSER.
Note: The rule of thumb is double your MAXTASK value to get the PROCUSER value.
MAXTASK of 500 in CA XCOM will require a PROCUSER of 1000. For example, if using CA Top Secret:
TSS ADD(acid) PROCUSER(1000)