Hmmm....
Two issues. Not sure how it's gone this long without someone finding them, but fortunately they are only in the sim and not in the PLC.
1. When a file is open and the sim is switched to program mode there is a hard crash. This may manifest as the sim closing unexpectedly.
2. The FilePointer and EndOfFile fields are not being properly updated.
Because the EndOfFile never gets set, the program overruns the string array you've set up, which then causes comm errors from reading beyond the array limit.
Both were easy fixes. We're dropping a maintenance release next week, so this fix will be in it.