This is a corrected version of the original DCS A-10C-Training-Maverick mission.
In the current version, you are expected to open the MAV page on the right MFCD, but in this mission the MAV page is not accessible from that side. This modified version changes the commands to use the left MFCD so you can get past this error. The voice-over will still refer to the "Right MFCD", but the highlights will be on the left MFCD buttons. Everything past this point in the training mission appears to work using the left MFCD.
For ease of use, put this corrected mission file in your ..\Saved Games\Missions folder, not the DCS World\.. folder.
NOTE: It appears that some people have a DCS-corrected version of this mission as part of their install, but even though I have the latest version of DCS, the mission is still incorrect, so I'm guessing others have this same issue. If someone posts their DCS-corrected version here I will remove this one. I've also learned that when you get to this point in the uncorrected mission, you can press and hold one of the lower OSBs on the right MFCD until the menu appears. You can then select to display the MAV page on the right MFCD.