[Slyk]

Did you try compiling WITHOUT that box to be sure it IS that box giving the error? I've had the same problem and they're tough to pinpoint sometimes. Worst case you may need to resnap a lot of brushes or even copy and paste into a NEW map file. That happened to me, couldn't fix the error and copied/pasted everything untouched into a new file and it was fine. IF you have to do that, prefab all you can.