Crash trying to launch on with a skeleton with Virtual Bones

Assertion failed: GetSkeletonVirtualBoneGuid() == GetSkeleton()->GetVirtualBoneGuid() [File:E:\Release\Engine\Source\Runtime\Engine\Private\Animation\AnimSequence.cpp] [Line: 261] Attempting to cook animation 'AnimSequence /Game/Characters/UE4_Guy/Animations/Crouch_Idle_Rifle_Ironsights.Crouch_Idle_Rifle_Ironsights' containing invalid virtual bone guid! Animation:{0x00000000,0x0000,0x0000,{0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00}} Skeleton:{0xC6207C05,0x41CB,0xAA38,{0x4F,0x72,0xC6,0xAC,0x41,0xE7,0xE4,0xAF

UE4Editor_Engine!UAnimSequence::Serialize() animsequence.cpp:261 
UE4Editor_CoreUObject!FArchiveSaveTagExports::ProcessTaggedObjects() savepackage.cpp:994 
UE4Editor_CoreUObject!FPackageExportTagger::TagPackageExports() savepackage.cpp:3212 
UE4Editor_CoreUObject!UPackage::Save() savepackage.cpp:3784 
UE4Editor_UnrealEd!UEditorEngine::Save() editorengine.cpp:3966 
UE4Editor_UnrealEd!UCookOnTheFlyServer::SaveCookedPackage() cookontheflyserver.cpp:2962 
UE4Editor_UnrealEd!UCookOnTheFlyServer::TickCookOnTheSide() cookontheflyserver.cpp:2166 
UE4Editor_UnrealEd!UCookOnTheFlyServer::Tick() cookontheflyserver.cpp:770 
UE4Editor_UnrealEd!FTickableEditorObject::TickObjects() tickableeditorobject.h:17 
UE4Editor_UnrealEd!UEditorEngine::Tick() editorengine.cpp:1195 
UE4Editor_UnrealEd!UUnrealEdEngine::Tick() unrealedengine.cpp:371 
UE4Editor!FEngineLoop::Tick() launchengineloop.cpp:2859 
UE4Editor!GuardedMain() launch.cpp:152 
UE4Editor!GuardedMainWrapper() launchwindows.cpp:126 
UE4Editor!WinMain() launchwindows.cpp:202 
UE4Editor!__scrt_common_main_seh() exe_common.inl:264 
kernel32!<Unknown> 
ntdll!<Unknown>