probably there is a problem with the object data, make sure that u didnt change anything to a wierd value, negative values or very high values can cause this.
to Sp4WnEd: obviously if the map doesnt work on single player then it wont work multiplayer, or maybe i dont get what u mean.
I also had a problem that made my map crash and I went all furious because I spent an awful lot of work into it. However I found out that I had imported an invalid .blp or .mdl file that made wc3 crash as soon as it was to be loaded. I suggest looking at your imported files and maybe remove and later re-import them. For my part it worked, Good luck,