It is strange that you have not tried to identify your problem.
1) First at all, start lobby with your teammates on different map's. If any map that you play didnt start, and at the forum there is no any question about it, then problen on your side.
2) If different map's starts only on few player's, then probem is on their side
3) it may be problem on CNCNet side, like download error or etc. Or player's have slow internet. Few restart help.
If all map's starts correctly, then dismember the problem. Strange, that u didn't describe the error - it is white screen, of internal error, or anything.
By your text look's like other's players didn't load, you just start multi map in solo and instantly win.
If it is not a punct 3) error, then of course, it is a .map file makes error. Map file has map, triggers, actions, unit statistic etc. With wrong trigger's if even your game start's in solo player not the fact that game will runs in multi, most of trigger's usable only for one player. You need to explore the problem with file.
1) First of all, clear the all of unit statistic, trigger's, actions etc like that, only clearly map. Make sure that map has a player start positions.
If map didn't load at this stage, may bee it is damaged. Make same one (in Final?) without anything and try to start with it.
2) If map start's correctly without modding, look's like u use triggers. Study ModEnc.
Good luckю