[Murph]

One thing to watch out for is that the mission name matches the name used in the config.ini exactly ( I assume use mean with the QMB+). For example;
If config.ini reads-
CustomXX=Zuti_Slovenia_Off_S
Then the mission must be called-
Zuti_Slovenia_Off_SBlueNone00.mis
Make sure the mission file includes the "00" at the end.
If you are trying to make single mission, I think you can call it whatever you wish.
Is the game's FMB saving the mission?