Thanks for the replies!
Well I have tried doing different things in the WT setup, but always so that I have the 20480 as the size. So I've done it like 2048 with a multiplier of 10, or 5120*4. I haven't tried messing around with offset options though. The reason for this is mostly because I have to re-install Visitor from scratch to get it to work again.
I'll try using a different size in the texture layer option, even though I doubt that would solve anything, since my map will load perfectly before the use of World Tools. This also goes for manually putting in trees. The issue only arises after I use WT.
To add to that: If I delete all the objects that I imported, the map will load again.