Hey Stalker!
I have a suggestion and a comment..
The suggestion is to try contacting the Mission Designers.. They might be able to help you since it's their mission... Rubble_Maker and CarolCray made it, I believe. However, they probably have a disclaimer in their readme that it's not their responsibility.. (as all mission designers should) So, I'm not saying to expect help, but they might be able to...
The comment is that I got the same error message when I tried to use Kegety's Resistance Editor Upgrade the first time.. (this was the first version, that error has since been corrected in the new version, according to a thread in the old forum)
So... Does this mission require that addon? If so.. Did you get an old version of the editor upgrade possibly??
Hope this helps... Just a couple shots in the dark.. as it were.
;D