Does anybody know why I’m have errors here?
You might need all the following. Are you missing one of the following in the OpenDoor.cpp file:
#include "DoorSwing.h"
#include "Engine/World.h"
#include "GameFramework/Actor.h"
#include "GameFramework/PlayerController.h"
#include "Components/PrimitiveComponent.h"
Besides that, maybe the IDE was not caught up yet and GetMass() should be returning a float.
If it builds fine, its OK too - you can see a red line without a direct header and its possible to build and work just fine.