EXECUTION_RESULT_ERROR

[Martus22]

I'm trying to run an example simulation (hello-pt-tb) from the example's NVFlare github and I get this error:

2023-10-18 10:58:57,320 - ServerRunner - ERROR - [identity=simulator_server, run=simulate_job, wf=scatter_and_gather, peer=site-1, peer_run=simulate_job, peer_rc=EXECUTION_RESULT_ERROR, task_name=train, task_id=ef15004e-e989-44d8-9cff-6c6852815657]: Aborting current RUN due to FATAL_SYSTEM_ERROR received: Result from site-1 is bad, error code: EXECUTION_RESULT_ERROR. ScatterAndGather exiting at round 0.

Yesterday I did the same simulation (same dataset and same .py) and it worked correctly so I don't know what has changed.
I would like to know what is happening. Thank you