Right click on the game in the library. Click local files. Click verify the integrity of game cache. Or something like that.
Deathtrap the same has happened to me. Have you gone into the files on any other ETW Game because I tried changing my flag in Medieval 2 it worked but now it just stays on that screen.
This could help. http://www.twcenter.net/forums/showthread.php?t=238484&highlight=madboris workaround