Window Command Error

[WillH3iZ]

I need help with this error I keep getting. I don't understand what it means.
I imported the Quests V1.1 script in with the paragraph formatter-the error I get
says: "Window_Command'line 22:NoMethodError occured.
        undefined method `size' for nil:NilClass
I'm not very good at scripting, but I understand the basics.
Thanks

Also are these scripts compatible with any other scripts other than Dargor's Custom Commands?
I'm using these scripts if it helps:

-KGC_ForceStopVictoryME
-KGC_Dash_8DirMove
-KGC_MiniMap
-KGC_CategorizeItem
-KGC_AddEquipmentOptions
-KGC_SkillCPSystem
-KGC_UsableEquipment
-KGC_EquipLearnSkill
-KGC_PassiveSkill
-KGC_Steal
-KGC_TargetExtension
-KGC_ClassDetailSetting
-Enu's Sideview Battle System
-Game Over Enhanced
-Ccoa's Small World Sprites
-Scene Title Screen Miria V1.0
-MOG_Location_Name_VX V1.0
-Neo Save System III
-KGC_LargeParty
-Display Victory Aftermath
-Scene Status ReDux