I was able to successfully convert the small door to a blueprint but every time I run the game it crashes! Once more, when I open the unreal editor (after a crash) I get an error that it could not load the door resource. If revert to the version immediately before the blueprint everything works fine. Something about the blueprint is the problem. Any ideas what???
Almost all my crashes so far have come from places where I was expecting the editor to link an actor into a UPROPERTY in my C++ code, but then I deleted or forgot to link in the actor.
When that happens, I find it helpful to:
- Inspect the details of actors that have my C++ components on them, and make sure their UPROPERTY references are filled in.
- Check the log (in
BuildingEscape/Saved/Logs), looking for a source file and line number in my code. That usually gives me the null pointer I’m dereferencing.
Don’t worry, there’s a technique for avoiding this somewhere in Section 3, so it won’t always be like this on every project. 
Thanks! Turns out the “PressurePlate” was unassigned hence causing the crash. I forgot to protect against that.