Having the same problem here. When I tried to start a QMB mission featuring the MiG-17A, the mission loaded to a point, then stopped with a message saying "Mission loading failed: null." Here's what the logfile says about the same attempt:
Loading mission QuickQMBPro/BAT_Aleutians/BAT_Aleutiansrednone00.mis...
Y=1940 / M=11 / H= 12 , Temperature - 0m = 2.0 .
Loading map.ini defined airfields:
Load bridges
Load static objects
##### House without collision (3do/Tree/Tree2.sim)
##### House without collision (3do/Buildings/Port/Floor/live.sim)
INTERNAL ERROR: Str2FloatClamp() - Clamped 5 -> 2 (delta = -3) to Range 0..2
INTERNAL ERROR: Str2FloatClamp() - Clamped 2e+006 -> 1e+006 (delta = -1e+006) to Range 0..1e+006
Mission error, ID_04: java.lang.RuntimeException: Zero Square processed from com.maddox.rts.SectFile@47370e
java.lang.RuntimeException: Zero Square processed from com.maddox.rts.SectFile@47370e
at com.maddox.il2.fm.Squares.load(Squares.java:83)
at com.maddox.il2.fm.FlightModelMain.load(FlightModelMain.java:723)
at com.maddox.il2.fm.FlightModelMain.<init>(FlightModelMain.java:1129)
at com.maddox.il2.fm.FlightModel.<init>(FlightModel.java:132)
at com.maddox.il2.fm.AIFlightModel.<init>(AIFlightModel.java:20)
at com.maddox.il2.ai.air.Maneuver.<init>(Maneuver.java:606)
at com.maddox.il2.ai.air.Pilot.<init>(Pilot.java:107)
at com.maddox.il2.fm.RealFlightModel.<init>(RealFlightModel.java:89)
at com.maddox.il2.objects.air.Aircraft.setFM(Aircraft.java:1686)
at com.maddox.il2.objects.air.Aircraft.setFM(Aircraft.java:1674)
at com.maddox.il2.objects.air.Aircraft.load(Aircraft.java:2073)
at com.maddox.il2.game.Mission.loadAir(Mission.java:1288)
at com.maddox.il2.ai.Wing.load(Wing.java:144)
at com.maddox.il2.game.Mission.loadWings(Mission.java:1078)
at com.maddox.il2.game.Mission._load(Mission.java:653)
at com.maddox.il2.game.Mission.access$600(Mission.java:123)
at com.maddox.il2.game.Mission$BackgroundLoader.run(Mission.java:409)
at com.maddox.rts.BackgroundTask.doRun(BackgroundTask.java:155)
at com.maddox.il2.game.MainWin3D.loopApp(MainWin3D.java:108)
at com.maddox.il2.game.Main.exec(Main.java:422)
at com.maddox.il2.game.GameWin3D.main(GameWin3D.java:235)
null
java.lang.NullPointerException
at com.maddox.il2.game.order.OrdersTree.getSection(OrdersTree.java:627)
at com.maddox.il2.game.order.OrdersTree.missionLoaded(OrdersTree.java:567)
at com.maddox.il2.game.order.OrdersTree.missionLoaded(OrdersTree.java:531)
at com.maddox.il2.game.Mission._load(Mission.java:762)
at com.maddox.il2.game.Mission.access$600(Mission.java:123)
at com.maddox.il2.game.Mission$BackgroundLoader.run(Mission.java:409)
at com.maddox.rts.BackgroundTask.doRun(BackgroundTask.java:155)
at com.maddox.il2.game.MainWin3D.loopApp(MainWin3D.java:108)
at com.maddox.il2.game.Main.exec(Main.java:422)
at com.maddox.il2.game.GameWin3D.main(GameWin3D.java:235)
[Apr 21, 2019 6:04:47 AM] -------------- END log session ---------
This only happens with the Mig-17A. Later-model MiG-17s work fine.