Perhaps try deleting the previously exported map files, then try exporting the map again? Sometimes that may work, as well as just exiting (make sure you save) FH and then re-launching it again.
If that doesn't work, then perhaps you may be missing a vital piece of your map such as a .map file, etc; it's best to check this if you accidentally have deleted any of these. The last reason I can think of is that there is either a mesh or a particle that is not exporting properly - perhaps due to missing files of itself - causing the map to fail exporting. In that case, try looking through your files to see if you can find which one may be causing the problem and either restore the missing file(s) and or delete the object from your object group.
I hope this is what you mean.