there's no point posting a particular mission, mate.
i've gone through every single stock single mission as well, and they either result in mission failed null error, or the mission starts with the horizon screen you normally get if there's a missing cockpit or weapons.
any plane, stock or modded, any mission, stock or modded, any map, etc...all ends the same way.
i'll post up my folder contents soon, and although it may seem a lot, it's really mainly planes -
remember, i have disabled all ETO planes in this install, so i only really have the Pacific planeset, and the planes in the list.
repeat, though - i did nothing, added nothing, when this suddenly started happening.
prior to this, i played a mission, as i said, in QMB. when the mission ended successfully, i changed the map and then got the null fail.
nothing else was changed at all, just the map.
then, the null error appeared, and it hasn't left since. it's now permanent, all maps, all planes, etc...
here's my folder, many planes, but other than that, mostly straight 3do stuff - i've tried to keep the classfiles to a minimum, but i do not think this is a memory issue, as this install was running much better and more stable than most of my other recent versions, and it definitely looks like a weapons/loadout issue, from the symptoms and the error log.