When I try to select terrain I get ERROR.

[KPC]

When I try to select terrain in editor it instantly closes and shows that error:

->

I don't know how to fix it. When I do it in new map it is ok (semetimes). When i open any another map the bug comes back. Also in melle maps when I try to copy/paste terrain. In custom maps bug
appears especially often (always) when I'm trying to select area.

 

[Warseeker]

Maybe this might help you :
[Crash] - WE Crash when marking terrain
Patch destabilized map

 

[KPC]

Ye this is it, thx a lot man.