Hmm...
First, I would recommend going into Map Maker and saving your map in another name. (If it was ZombieMap, make it Zombie.Map, or something like that).
Then, export the new, duplicated map, and see if that helps.
If this doesn't work, write down a list of the FHO files that were exported.
When you've done this, go to FeralHeart>>Media>>Objects, and copy+paste the files you had written down into your Exports folder. Click yes if it asks to replace.
This will be a kind of manual export of your map's FHO files, and may help resolve the issue. Re-send the map files and the newly exported FHO files to a friend, and have them test it.
If it still doesn't work for you, it's possible that you have too many objects placed into your FHO files. If this has happened, I suggest using Object Maker to create new FHO files, and move some of the objects from your map into these. You may have to replace some of these objects in your map, but I've seen this happen several times before.
If this is the issue, make sure you aren't going over about 25 items per FHO/Object file.
I hope some of these help ya