I downloaded the MiG-21 pack along with all the necessary requirements, but now my game won't load. The blue circle spins for a bit, and the thing pops up on the screen but disappears after about 5 seconds.
[2:43:52 AM] FM called 'FlightModels/P-11c.fmd:PZL_P11' is being loaded from Alternative File: 'pzl_p11'
[2:43:52 AM] FM called 'FlightModels/MiG-15F.fmd' is being loaded from Alternative File: 'gui/game/buttons'
[2:43:52 AM] FM called 'FlightModels/MiG-15F.fmd' is being loaded from Alternative File: 'gui/game/buttons'
[2:43:52 AM] FM called 'FlightModels/MiG-15F.fmd' is being loaded from Alternative File: 'gui/game/buttons'
[2:43:52 AM] FM called 'FlightModels/MiG-17.fmd' is being loaded from Alternative File: 'gui/game/buttons'
[2:43:52 AM] FM called 'FlightModels/MiG-17F.fmd' is being loaded from Alternative File: 'gui/game/buttons'
[2:43:52 AM] FM called 'FlightModels/MiG-17PF.fmd' is being loaded from Alternative File: 'gui/game/buttons'
[2:43:52 AM] Main begin: PlMisAir(GUIQuick): class ' air.MIG_21F ' not found
[2:43:52 AM] java.lang.RuntimeException: PlMisAir(GUIQuick): class ' air.MIG_21F ' not found
[2:43:52 AM] at com.maddox.il2.gui.GUIQuick.fillArrayPlanes(GUIQuick.java:3167)
[2:43:52 AM] at com.maddox.il2.gui.GUIQuick.<init>(GUIQuick.java:3613)
[2:43:52 AM] at com.maddox.il2.gui.GUI.create(GUI.java:160)
[2:43:52 AM] at com.maddox.il2.game.Main3D.beginApp(Main3D.java:1885)
[2:43:52 AM] at com.maddox.il2.game.Main3D.beginApp(Main3D.java:1579)
[2:43:52 AM] at com.maddox.il2.game.MainWin3D.beginApp(MainWin3D.java:212)
[2:43:52 AM] at com.maddox.il2.game.Main.exec(Main.java:432)
[2:43:52 AM] at com.maddox.il2.game.GameWin3D.main(GameWin3D.java:235)
[May 27, 2020 2:43:52 AM] -------------- END log session -------------