Age of Empires 3
Try opening the XML files in your Internet Browser. You might be able to edit them from there.
If you can't access the file, make sure you are running as administrator. Also -- make sure the file is not set to Ready Only so you can actually make changes.
Oddly enough changing the proto.xml in the game directory used to work perfectly fine until I updated to the retail version V1.14 (which is not the live online version, but the boxed latest)
So then I tried changing it in the My Documents/Games/Microsoft etc section, and when I did that, when I started a skirmish I had nothing but a town center!
Feel free to delete this one.
[Edited by Nocturne4ever, 1/2/2012 2:28:10 PM]