Usually uninstalling and deleting the entire game and folder works.
Sometimes this FeralHeart.exe error message can occur when you are trying to get into a crowded map like Fluorite. If this is the case just keep trying until you can get in, or just use the character reset option at the top right of the forum and get your character to a less crowded region.
You can also try going into the game's options through the main menu and then go into video settings.
From there you can:
Set Anti Aliasing to 0
Turn Water Reflection off
Set View Distance to 0
Changing your rendering system between OpenGL & Direct3D9
Also if you've ever downloaded any mod(s) at some point files could have been deleted or rearranged. Sometimes double particles appear in you particle folder. If you do find double particles delete the duplicates.
If all else fails maybe try refering to this:
http://www.feral-heart.com/index.php?option=com_jfusion&Itemid=2&jfile=index.php&topic=26735.0Can't think of anything else right now but I hope something here works. Goodluck.