Skrit has explained your entire problem.
QUOTEhas to be multiplyable by 32.
32
64
96
128
160
192
etcUNQUOTE
(Yes, I know my quoting skills fail, No, I wont click Go Advanced or Add Reply).
The map HAS TO BE a multiple of 32, that's IT. If you have downloaded WEU you STILL have to have it be a multiple of 32 but the maximum size has increased.
Do you understand, or not? It's pretty self explainable. I understood the message just fine back in RoC (I think you could extend the bounds in RoC, yeah?).
And if you don't know HOW, it's under the Scenario Tab in the Terrain Editor (main part of the WORLD Editor). The Scenario tab has one option that allows you to change the size of the map in both Camera and Map bounds. Check both Camera and Map Bounds and select any direction up to 8 times in order to extend it by 32 (pressing it once increases the bounds by 4, but HAS to be a multiple of 32).