A map will sometimes crash upon attempt to export for several reasons:
-The map is too large
-There are an overload of items it's trying to export
-Your computer simply can't handle it (uncommon)
-There are duplicates in your media folder*
-Meshes you downloaded were loaded in the object maker and saved to a Default group rather than their own group. (Default groups include My Plants, My Rocks, etc.)
*Check your media folder, look in particles, textures, terrains, etc. Anything ending with a _0 or _1 needs to be deleted. Often it's a problem with particles.
If I may ask, what are your map's dimensions?