ARS0188E - IBM Content Manager OnDemand server issues the message "ARS0188E Unable to create thread. The return code is X" and exits.
Unfortunately ARSSOCKD ends without enough diagnostic information to tell where the issue was.
Starting at 10.5.0.8 CMOD on z/OS, instead of just terminating, now ends with a dump.
Support can analyze the dump and should be able to localize the root cause.
Ed