Just stumbled onto this problem the other night. Am hoping I'm not the only one <grin>, so I'll put down what I've done and if a couple of ya can try it please post if you too get an error.
Basically I loaded up the "RED - Buffaloe VS Zero" mission in the "pf_upgrd0013/Singapore1" directory. This mission generates fine and you can tweak the two flights as you wish. However, my squad wanted to add an additional flight of zeros. So if you go to the BLUE squad slot 2 and duplicate the settings for the A6M2-21s and just add 3 to keep it simple (I've found it doesnt seem to matter). Try generating the mission.
I get an "error when writing some of the ground objects" every time. I've tried different plane slots for both RED and BLUE and it happens every time. IF I change the map . . . . . . . it works fine! I used Okinawa.
As I requested, if this is happening to you too . . . please post so I know I'm not the only one. I sent an email to UBERDEMON via the addy that is listed in the error message but no reply as yet. I just found this forum so I figured I'd post here too.
L8R