GoogleVR 2D Widget's problem, please help

hello, i am making a VR game and i just simply want to create a widget animation or just a static image when triggered some event, but when i package it for Android(ATC), it failed because of the widget i created and place it on any of the blueprint that will create the widget.

when i looked into my log, i saw that error about dependency Index.

0]LogWindows:Error: Assertion failed: !DependencyIndex.IsNull() [File:D:\Build++UE4+Release-4.13+Compile\Sync\Engine\Source\Runtime\CoreUObject\Private\UObject\SavePackage.cpp] [Line: 4366]

and this one as tells which blueprint has that error…

Failed to find dependency index for WidgetBlueprintGeneratedClass /Game/MobileStarterContent/UMG/test.test_C (Function /Game/MobileStarterContent/Blueprints/BP_key.BP_key_C:ExecuteUbergraph_BP_key)

is there anyway i can fix that? or is there a better way to replace it? everything in my game works fine expect the widget, they works fine in editor but it caused the package fail, should i update my codeworks? or change something in the .cpp file?