This crash has been logged due to high frequency among our users.
I have tested in 4.15.2 based on the user comments below, but have been unable to reproduce this issue. In my attempts the Blendspace handles animations being force deleted.
User comments
repro steps currently unknown
Access violation - code c0000005 (first/second chance not available) UE4Editor_Engine!UBlendSpaceBase::UpdatePreviewBasePose() [blendspacebase.cpp:1220] UE4Editor_Engine!UBlendSpaceBase::DeleteSample() [blendspacebase.cpp:827] UE4Editor_Persona!SBlendSpaceEditorBase::OnSampleRemoved() [sanimationblendspacebase.cpp:105] UE4Editor_Persona!TBaseSPMethodDelegateInstance<0,SBlendSpaceEditorBase,0,TTypeWrapper<void> __cdecl() [delegateinstancesimpl.h:327] UE4Editor_Persona!TBaseSPMethodDelegateInstance<0,SBlendSpaceEditorBase,0,void __cdecl() [delegateinstancesimpl.h:434] UE4Editor_Persona!SBlendSpaceGridWidget::OnKeyUp() [sanimationblendspacegridwidget.cpp:679] UE4Editor_Slate!<lambda_6edabb7999d104566d200ed4979fb141>::operator() [slateapplication.cpp:4738] UE4Editor_Slate!FEventRouter::Route<FReply,FEventRouter::FBubblePolicy,FKeyEvent,<lambda_6edabb7999d104566d200ed4979fb141> >() [slateapplication.cpp:238] UE4Editor_Slate!FEventRouter::RouteAlongFocusPath<FEventRouter::FBubblePolicy,<lambda_6edabb7999d104566d200ed4979fb141>,FKeyEvent>() [slateapplication.cpp:220] UE4Editor_Slate!FSlateApplication::ProcessKeyUpEvent() [slateapplication.cpp:4736] UE4Editor_Slate!FSlateApplication::OnKeyUp() [slateapplication.cpp:4705] UE4Editor_Core!FWindowsApplication::ProcessDeferredMessage() [windowsapplication.cpp:1613] UE4Editor_Core!FWindowsApplication::DeferMessage() [windowsapplication.cpp:2120] UE4Editor_Core!FWindowsApplication::ProcessMessage() [windowsapplication.cpp:867] UE4Editor_Core!FWindowsApplication::AppWndProc() [windowsapplication.cpp:714] user32!UserCallWinProcCheckWow() user32!DispatchMessageWorker() UE4Editor_Core!FWindowsPlatformMisc::PumpMessages() [windowsplatformmisc.cpp:980] UE4Editor!FEngineLoop::Tick() [launchengineloop.cpp:2977] UE4Editor!GuardedMain() [launch.cpp:166] UE4Editor!GuardedMainWrapper() [launchwindows.cpp:134] UE4Editor!WinMain() [launchwindows.cpp:210] UE4Editor!__scrt_common_main_seh() [exe_common.inl:264] kernel32!BaseThreadInitThunk() ntdll!RtlUserThreadStart()
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-44939 in the post.