I'm having this exact same problem and I don't believe a solution has ever been posted here. It appears that others have this issue as well. I'm running XP (SP2) and have plenty of HD space. Only a 1g processor and I don't have that much RAM ~.5g, but others with the same problem have plenty, so I doubt it's related to that. (I'm also planning on upgrading the RAM in the near future anyway) I think they may have been running Vista, so it seems to effect different OS versions. Yes, I loaded the mod first, it says GEM in the top right.
Poster #28 had this problem as did #32 Sepulchre. I did what you said in #29 even though I have version 4.1 not 4.08 of your map. There is nothing after "ModPath=" in line seven. However, I noticed that "GiantWorldMap v4.1" is located in Giant Earth Map\PrivateMaps not Giant Earth Map\PublicMaps as you mentioned earlier. I doubt that is the cause because we can choose the map but crash when we get to the leader select screen.
Sepulchre came back later in #54 and said installing it in the My Games directory fixed his problem. I tried that as well and it still crashes. Sepulchre, did you do anything else different?
#61 also had this issue. As soon as I finish this post I'm going to copy the map file into a new PublicMaps folder within the Giant Earth Map directory because the download didn't include such a folder. I just downloaded a few hours ago btw.
Heh, I hope I've been thorough enough.
EDIT: I just checked again and I don't have 3.13 installed, could have sworn that I did. So, I'll post back to let you all know if it was the problem. I have a feeling it was, and I have a feeling that the other people with the same issue probably thought they had 3.13, too. Goes to show you that it doesn't hurt to actually go and check.
EDIT2: Just tried it with bhruic's patch, same error. will now attempt with the official patch instead.
EDIT3: Well, that wasn't the problem. I get the same error using either version of the 3.13 patch. C'est la vi. Anybody have any other ideas?
EDIT4: Ok, got it to work, well, at least I got the leader choice screen to load. I didn't go any further because I don't have time to play right now and I wanted to comment here. For anyone who was having the same problem tis is what I did: uninstalled/reinstalled BTS, downloaded the 3.13 patch separately (you can find a link on these forums) and then installed it.