Did you perhaps remove limbo.are? If so, you need to put it back. Mob #3 is your "supermob" which is a required element for Smaug mudprogs to work right.
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"The past was erased, the erasure was forgotten, the lie became truth." -- George Orwell, 1984
You can still make areas that don't load with the Area Editor, do an 'area check' to make sure all mobs exist.
You can open the area.lst file with the Area Editor, that will open all areas, and then the checks for mobs etc. work much better, because some areas use things that are in other areas. By opening all areas you should minimize the number of warnings in the area check.
Another thing I noticed, is that it always gets errors from the existing areas with smaug, I was going to look at those to see if I could spot what I was doing wrong.
Sounds like you are referencing a non-existent mob. Perhaps you have a reset for a mob that doesn't exist? Try downloading the area editor from this site, and running an area check on your new area.
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