FRUA has been weird recently with all the bugs. The event that gives you the key was missing...which is strange, given that I was able to successfully playtest the module to completion prior to uploading it.
I've uploaded a fixed version of the module to the beginning of this thread and will upload to the usual locations right after I type this reply.
Here's the issue, though...if you've already had the lever pulled in the dungeon, there's no way you can get that key now. What I suggest is that you go into the editor, remove an event you've already completed (since that map has 100% of the events used) and add one to give you Key 1 (Brass, by default, I think). That should get you past the door.
Thanks for pointing out the issue. Don't know how it happened, though.