Sometimes while exporting, the game may freeze for a few moments. It's in these few moments that I've learned you cannot click the screen no matter what. For some reason this causes crashing. If you clicked the screen at least once, then I'm afraid reinstalling the game would be the way to go
However, if you didn't click the screen, make sure you do not have any duplicate particles (files ending in _0, _1, etc) in your "particles" folder. Some other things that may help would be to lower your view distance and turn off water reflection just before you jump into the portal (only temporarily, just to help reduce lag so crashing becomes less likely). Sometimes sky and weather files cause crashing too, so it might be worth deleting those