I have the exact same problem. However, I have gotten the game to run with Wanderer's Edition working, but not through Steam. Starting the game via Steam or Nexus Mod Manager results in GFWL starting (which FOSE should disable, so you know it's not worked correctly) and the same error message you get. However, if I navigate directly to my Fallout 3 folder within steam apps/common and active the FOSE.exe from there (which I have renamed to fallout3launcher.exe) Fallout will launch without GFWL appearing, no error message once entering the game and all appears to be working as it should. You do not however, get the time logged playing in Steam. I also have Steam installed in my program folder, I was going to move it, but your post makes me think this will not help. Any suggestions would be appreciated.....