Uninstall all of your mods (everything) and start a new game -- do *not* load a previous game, this is very important. Now quickly play up to the point where Imoen joins again, and if everything goes well, as it should, then quit the game and begin to install your mods ONE BY ONE. Start with Baldurdash, then start a new game, and zip through as before, up to the point where she joins. Do this, remembering to add things one by one, until your game acts up again. When it does, the last thing you installed is the culprit. If it doesn't act up, and everything goes smoothly, it can probably be chalked up to a botched install.