Sometimes weird things can cause my map maker to crash FH and no longer work, I'm assuming it can be anything from objects to a messed up terrain/mask file or even a .fhm in terrains.
I'd suggest cleaning out things one by one that you may have downloaded/made recently, possible install a second FH (name it FeralHeart 2 to not overwrite the other one) and move anything you need over to that FH or re-install and replace the old one.
Only suggesting downloading a second FeralHeart to possible find the issue when moving things over. ;o