Turns out the problem is something to do with multi-tile buildings, such as the 2x2 tile Sentry Tower. When it goes to load a multi-tile building, it crashes and says that the object it was trying to plot on the map doesn't even exist... Well, nothing another cup of coffee and staring at code won't eventually fix...
Here's two pics. One's a screenshot from my game, showing some infantry and two vehicles I've just added to my game (with a Wildfire MAU behind them just because I like seeing how big they are next to people!).
The other is one of the computer generated artworks I'm using as loadscreens between levels in the game. Basically, I've been rendering 3D scenes, then applying different Art Effects to the bitmaps in Corel Photopaint to give them an arty look. The effects add lots of details to the picture that make the MAUs looks much more interesting than the original 3D renders.
I also added a mobile ECM truck to the game today. Basically, you park them somewhere, and the closer an enemy units gets to the truck, the worse their targeting computers behave, and the harder it is for them to detect your units with their sensors. Of course, it doesn't effect visual unit detection, only electronic sensors, and it wouldn't have an effect on units that don't use targeting computers, ie, infantry who just point their rifles and fire, or some highly skilled MAU pilots who can manually target enemies without needing the aid of a targeting computer.