Hi Bruce, The call stack says you called MPI_Intercomm_create​. Try get a full stack trace using debugger. -- Hui ________________________________ From: Palmer, Bruce J via discuss <[email protected]> Sent: Wednesday, March 30, 2022 6:28 PM To: [email protected] <[email protected]> Cc: Palmer, Bruce J <[email protected]> Subject: [mpich-discuss] Error message Does anyone have any idea what the following error message is supposed to be telling me? It appears to be coming from an attempt to make a copy of MPI_COMM_SELF using MPI_Comm_dup. Abort(66703622) on node 4 (rank 4 in comm 0): Fatal error in internal_Intercomm_create: Invalid rank, error stack: internal_Intercomm_create(134): MPI_Intercomm_create(comm=0x84000005, 0, comm=0x84000003, 3, 0, newintercomm=0x7fffffffcd68) failed internal_Intercomm_create(102): Local and remote leaders must be different processes Bruce Palmer