Not surprising. You're trying to load the mission in a version of FS2_Open that is over 6 months older than the build of FRED that you used.
You should always use a build of FS2_Open that is as old or newer than the version of FRED you used. The other way round is pretty likely not to work.
Wha???? :mad:
I feel like I'm going around in circles now. You gave me the latest build for FS2_Open here: http://www.hard-light.net/forums/index.php/topic,38448.0.html
Then you gave me the latest build for Fred2 on this thread.
Now you're telling me that the latest build of Fred2_Open is 6 months ahead of FS2? This means my problems can't be fixed until someone releases a newer version of FS2_open!
*Gets ready to pull hair out*
Please tell me you have not been driving me around in circles... :(