When multiple Discrete Transfer simulations are run at the same time a conflict of the created rtrace-files can occur. The corresponding error message is Parallel run: Received message from follower ——————————————– Follower Partition: 64 Follower routine : SU_RADFLOW Leader Location : Message Handler Message Label : 666000013 Message follows below – : +——————————————————-+ | ERROR #666000013 has occurred in subroutlne SU_RADFLOW. | Message: | Partition 64 could not open file to store ray tracing data. | This partition may not have access or writing permission to the | default directory. Please try setting a different location for | the ray tracing data file under the Advanced tab of the Solver | Control panel in CFX-Pre. Keep in mind that all processes must | have access to the new location. +——————————————————-+ +——————————————————-+ | ERROR #001100279 has occurred in subroutlne MESG_RETRIEVE. | Message: | Stopping the run due to error(s) reported above +——————————————————-+ The background is that the rtrace files are written by default to the users home-directory. As this is the same for all jobs, a conflict can occur when multiple jobs run at the same time. This issue is fixed for 2021R2 and following. For 2021R1 and before the workaround is to set a specific directory for each job individually. This is achieved with the following CCL: FLOW: Flow Analysis 1 SOLVER CONTROL: THERMAL RADIATION CONTROL: RAY TRACING CONTROL: File Path = END END END END An alternative workaround is to apply an incorrect path on purpose in the above CCL: This results in the solver writing the rtrace-files into the temporary working directory .dir of the individual jobs. As mentioned, these workarounds will not be required with 2021 R2 ff. This error message can also be written if there are other problems writing to the rtrace files – see Solution 2031379.