It is possible to get the Out Of Memory error when not saving as well. It just happens the most when saving. GalCiv2 does attempt to determine if there is enough memory available before saving; it saves the size of the previous save game and asks for that amount of memory at the beginning of the next save. However, if it needs more memory, it has to ask for an increased amount, then copy all the currently saved data to the new memory. So if there's not enough room in memory for the current block of memory and the new one, the error will still occur mid-save.
Unfortunately, the memory management in GalCiv2's code base is almost nil. I'll be nice and not pick on the developer who wrote the 3D engine despite the fact that he no longer works here, but the fact is that we'd have to pretty much re-write the engine to get more control (or even more information) over the memory usage. I tried introducing the memory tracker that we're using for the fantasy game, but I couldn't even get Dark Avatar to compile with it, so it was pretty much a waste of two days during the 1.7 beta.
I'm not saying that I'm giving up on the out of memory issue, but I am saying that it's been incredibly frustrating for me to try and find the cause.
We're planning on putting up the 1.8g that's been up as a test build this week so that it at least takes care of the pathfinding issues and the metaverse error 12.