Saving level or compiling level blueprint crashes engine

I’m working on my first unreal engine 4.6.1 project - a small VR prototype with my Oculus Rift. So far it’s been going well and I’m really enjoying the unreal engine. However, since this morning whenever I try to compile the level blueprint, or save the level, the entire engine crashes. This means I can’t continue my project as I can’t make any changes. Even reverting my blueprints to the last working version (last night’s) hasn’t made a difference. I can compile/save my other blueprints just fine, only the level blueprint is the one that is causing crashes.

I can revert to the commit from 2 days ago and it works, but due to the binary uasset and umap files I can’t diff them to see what changed (one of many reasons I really wish these unreal engine project files weren’t binary - very revision control unfriendly).

When I crash I get the following rather cryptic stack trace:

MachineId:DA941A0049A73C50A6B6BBA21C75546C  
EpicAccountId:c0377db1e1ff4a12920e073413da61b7

Unknown exception - code 00000001 (first/second chance not available)

Assertion failed: TargetDelegate [File:D:\BuildFarm\buildmachine_++depot+UE4-
Releases+4.6\Engine\Source\Editor\UnrealEd\Private\Kismet2\BlueprintEditorUtils.cpp] [Line: 5407] 

KERNELBASE + 24684 bytes
UE4Editor_Core + 3092349 bytes
UE4Editor_Core + 1597688 bytes
UE4Editor_Core + 1479058 bytes
UE4Editor_UnrealEd + 9502651 bytes
UE4Editor_Engine + 5012673 bytes
UE4Editor_UnrealEd + 9881575 bytes
UE4Editor_Engine + 9941935 bytes
UE4Editor_CoreUObject + 1518587 bytes
UE4Editor_UnrealEd + 1780841 bytes
UE4Editor_UnrealEd + 2625915 bytes
UE4Editor_UnrealEd + 2613112 bytes
UE4Editor_UnrealEd + 6316416 bytes
UE4Editor_UnrealEd + 3247874 bytes
UE4Editor_UnrealEd + 3243162 bytes
UE4Editor_UnrealEd + 3240820 bytes
UE4Editor_LevelEditor + 570935 bytes
UE4Editor_Slate + 588774 bytes
UE4Editor_Slate + 1535133 bytes
UE4Editor_Slate + 1030727 bytes
UE4Editor_Slate + 1037049 bytes
UE4Editor_Slate + 1435577 bytes
UE4Editor_Slate + 2116506 bytes
UE4Editor_Slate + 2296435 bytes
UE4Editor_Slate + 432060 bytes
UE4Editor_Slate + 160583 bytes
UE4Editor_Slate + 832224 bytes
UE4Editor_Slate + 770598 bytes
UE4Editor_Core + 2484713 bytes
UE4Editor_Core + 2400763 bytes
UE4Editor_Core + 2489275 bytes
UE4Editor_Core + 2387186 bytes
user32 + 9268 bytes
user32 + 8855 bytes
UE4Editor_Core + 2490486 bytes
UE4Editor!FEngineLoop::Tick() + 3434 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.6\engine\source\runtime\launch\private\launchengineloop.cpp:2193]
UE4Editor!GuardedMain() + 479 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.6\engine\source\runtime\launch\private\launch.cpp:131]
UE4Editor!GuardedMainWrapper() + 26 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.6\engine\source\runtime\launch\private\windows\launchwindows.cpp:126]
UE4Editor!WinMain() + 249 bytes [d:\buildfarm\buildmachine_++depot+ue4-releases+4.6\engine\source\runtime\launch\private\windows\launchwindows.cpp:202]
UE4Editor!__tmainCRTStartup() + 329 bytes [f:\dd\vctools\crt\crtw32\dllstuff\crtexe.c:618]

Please help UE Answerhub, you’re my only hope!

EDIT: I have new information to add. I have one BP (not level bp) that dispatches a custom event. When I add the event node for this event to my level bp, the editor crashes as soon as I try to remove the event node from the level bp.