Do you have any Mod´s installed? If so, which ones?
Disable or better uninstall them and then
check your game with Steam. Test it again.
If there aren't too many, you can deactivate them one at a time until you find the guilty one.
To find other bugs, please upload a savegame here so we can test it. As you know, we need the -.ess and .-skse files to do this.
Please put them in an archive, because the forum does not support -.skse. You can find it here: ...\Documents\My Games\Enderal\Saves.
(if possible, no auto- or quicksaves, but saved manually)
PS:
Your error message was already
there once, where mods was the problem.