If you want to download offline missions, look for the MissionName.res file and download that to your missres folder. This is the new way of running offline missions. If no .res file exists you can download the .mis file (and any sound, bitmap, or other content), open it in the mission editor, and select Build off the File menu to create the .res file.
The offmiss folder is used when you edit a mission and is created by the Mission Editor.
- sudz