The "Build Res Library" menu option will create the res file for you. I'm not sure what you mean when you use the phrase "saved it to", but if you are using "Save" or "Save as..." to create the res file it won't work.
Enable your Explorer to show you file extensions so you don't just see 'Mis'. Copy the Mis.res file to the
missres folder off the game directory.
Then either make sure the current offline terrain is the same as the one used in the mission, or check the "Show missions for all terrains" checkbox to view the mission. Note that even if you do see the mission using the checkbox you will only be able to run your mission when the current offline terrain matches.
I'm very confused by these two phrases:
when I go offline to open the "practice missions" area it doesn't show up.
and
It does show in the "missions" area offline
But follow the steps above and you should be golden..
- Sudz