After deleting the files from server and client side I still get the same error. Of course I also tried reinstalling of the server, mods and game.
With ~60 mods I referred to the explicit map mods not all the mods I use. Im just curious what the problem here is and why that error only occurs when I exceed some specific map size. If I have some free time today I try to reproduce this with only map mods.
What I also see: the map can't even be initialized. It stays like it is shown in the image in the servertest directory.