I've changed the size of my maps to:

<iGridWidth>64</iGridWidth>
<iGridHeight>40</iGridHeight>

and now I get dark stripes on the right side of my worlds, they always start at mountains or hills

where could be the problem?

A map of this size is extremely ressource consuming (und will probably become unplayable slow in tha late game, even on a good computer) so perhaps the appearance of those stips has something to do with it...

without the BtS 3.13 Patch I had no such problem (it depends how u define unplayable :) i like this mapsize)

I think I had this problem once when making a larger map. I believe I just ignored it and it finally went away. :D I hope that happens with yours, too.