Hmm, does this map contain any particles by any chance? It's possible that there's double partiles in their Feral Heart folders when they installed your map. It's probably best to look for particles ending in _0, _1, and so on in the following folders:
- my_objects
- particles
- exports
If you do not see any there, try asking them to change their game's subrendering systems. You can do that outside of the game by: http://www.feral-heart.com/index.php?option=com_jfusion&Itemid=2&jfile=index.php&topic=43234.0 (http://www.feral-heart.com/index.php?option=com_jfusion&Itemid=2&jfile=index.php&topic=43234.0)
I'm going to download an see also.