Process Chain Execution aborts with U2004131 <Process Chain Name> is already in process through UC4 RunID '<RunID>'.
This can be an issue of the SAP Agent and therefore the first stop is to restart the agent and to rerun the job.
If restarting the agent, and troubleshooting has to continued ask the customer to provide the following
WP and CP log and trace files (tcp/ip=2 db=4).
The SAP Agent log file and trace file (tcp/ip=42 rfc=4).
The xml export of the job and of the SAP Connector.
The report of the job with runid mentioned in the error message.
Ther report of the jobs with raised the error message U2004131.
The exact version of your SAP system (Transaction SPAM ==> Package level ==> Screenshot).
Check the status of the concerned process chain with RSPCM transaction and provide a screen shot (with the problem ongoing).