I also ran into this problem using a new Big World installation.
I solved it by just spawning "Edwin" in another area (Where the scripts mentioned above aren't causing him to de-spawn instantly..) and then I could go on as usual
On my way to reinstall again I noticed something. Can this cause an error?
In the Big World Setup under the option 'Set resolution of the game' was checked and set to 1920x1080 : but when it got to the Widescreen-mod installation I went with 1280x720.
I 'cleaned' it in accordance with some of the suggestions on the forum. (Basically what you said)
What I did was when I had completely installed BG2+ToB+the newest patch (26498 not 26499) and started a new game for both BG2 and ToB, I copied the entire folder to another harddrive.
When I 'cleaned' it I deleted the whole folder with the modded game, then I copied the backup folder back in place netting me a cleaned install, correct?
Not sure how it managed to get corrupted then.. bad luck I suppose..