You can't load 'saved' missions for some reason. I posted on this under bugs but no-one has responded nor has it changed. In order to run a mission, you have to start from scratch.
The way to post a mission is one plane at a time. Create a plane set that you want, then 'save' it and 'submit mission'. Once the system takes the mission, then 'edit' mission, and add your next plane set. Keep repeating this process, one plane at a time, until you have everything in you want.
What you don't want to do is create a 5+ plane set and try to submit them all at once. Invariably there is a problem with one, ie. invalid weapons set, or 'no ordinace at airfield', then you have to start ALLLLL OVER from scratch again...grrrr..
You'll find there are some minor glitches as well. For example, if you change airfields after you have submitted mission, some of your planes might launch from hangers...don't know why, but they do. (then mission guys will say 'dude, you launched me from hanger')
Good luck.