Hi CK,
As you've been messing around with airfields I suggest you go into your main CFS2 file and delete the following files:-
INDEX_FILE
STR_INDEX
AIRWAY_INDEX
ICAO_INDEX
LAT_INDEX
WAYPOINT_INDEX
All your filelist.dat files
All your .cdp files
And the .cdp and filelist.dat files in any remote resource files that you may have.
All of the above WILL be re-generated by the sim on re-starting and/or using that resource.
Although you've checked, re-check carefully how many ac and ships you have, it seems (strangely?!) that everybody's sim reacts differently to different amounts. Remove ac (to a safe place) so that you have no more than say 75 (don't forget to check different camo versions within the same ac, which will increase the total amount of ac). Do the same with ships.
Re-start the sim and see if that does it. If not it still could be the amount of airfields, if you have huge amounts. If still probs and have have very large amounts of airfields, then start removing a number and see if this does the trick.
Fingers crossed you should have your QC and MB up and running again.
Cheers
Shessi