I got done enough with my first real mission to e-mail it to my brother for playtesting. He put the .pbo in the proper directory, fired up OFP, found it in the Single Missions list, and selected it. He got the loading screen, with the progress bar and the oscillating rectangle, but when the load was complete he was taken immediately back to the main game menu, without any sort of error message that he could see.
The mission works just fine for me. I have version 1.45, and he may have an earlier version, although he's not sure. One of the things I do in an init field is load a set of ammo boxes with a variety of weapons and magazines. They're not (unofficial) addon weapons, but we're speculating that one or more of the weapons is unknown in his version, so instead of ignoring the addWeaponCargo command, the mission aborts.
Does this sound reasonable? Does everybody already know exactly what causes this sort of behavior, and I'm barking up the wrong tree? I've never downloaded and installed a third-party mission myself, so I don't have experience with that.
Thanks,
Barak