I sure don't know what this would be. I am not home right now to test, but I tested the RCS version this morning and loaded into it several times. If you have just the map and just Thundr's RCS mod in your folder it should work. Are you using shaders?
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Edit: After lowering both the rcs densityMap_ground and fruits files it loaded.
Yes i have only the map and thundr's rcs and pf (tried disabling them), no i don't use shaders.I even tried lowring the densityMap_ground file to 8k but still im getting the same log errors. And as i said earlier im sure my pc can handle atleast loading rcs map.