The only immediately obvious difference between the trn file I received and the ones saved by my SP games is that the one from llamaserver has extended attributes.
This is my first time playing with llamaserver, so the help of more experienced players would be appreciated to resolve this problem.
I am not familiar with MacOS but it is more or less based on Unix, the program trying to access a file it has no rights over might be shut down by the system? Does your file has the right rights and/or owner/group? (man chown/chmod/chgrp for more info)
Just to confirm, you're running the latest patch level (Dominions 3.24) with CBM 1.6 enabled (in the mod preferences screen), correct?
One thing you could try: Put up your own 2 player test game on Llamaserver with just you and an AI and see if it works. Try it with this map, and maybe try one with a different map. Or you could try a local game on your machine with this map (I hope it's not the map!).