UE4Editor-Projectname.dll module missing

I am using UE 4.6.1. I am working through this tutorial, but have gotten stuck early on. After making changes to the header and C++ files in Visual Studio, I am no longer able to open my project in the Unreal Editor. When I try to open the project, I get an error message telling me that the module UE4Editor-Projectname.dll is missing or built with a different engine version. I am getting a lot of errors in Visual Studio, and I think the problem might be that the code isn’t linking in with the engine as it should. Most of the errors involve undefined identifiers.

Looking here, I saw that there is a second project in the solution explorer containing the engine itself. My solution explorer only contains the project files.

Advice on how to proceed would be appreciated. I’m a complete beginner to UE.

Edit: In case the problem is with my code, here it is:

FPSGameMode.cpp

#include "FPSProject.h"
#include "FPSGameMode.h"
#include "Engine.h"

AFPSGameMode::AFPSGameMode(const class FObjectInitializer& ObjectInitializer)
	: Super(ObjectInitializer)
{
 
}

void AFPSGameMode::StartPlay()
{
	Super::StartPlay();

	StartMatch();

	if (GEngine)
	{
		GEngine->AddOnScreenDebugMessage(-1, 5.f, FColor::Yellow, TEXT("HELLO WORLD"));
	}
}

FPSGameMode.h

#pragma once

#include "GameFramework/GameMode.h"
#include "FPSGameMode.generated.h"

/**
 * 
 */
UCLASS()
class FPSPROJECT_API AFPSGameMode : public AGameMode
{
	GENERATED_BODY()
	virtual void StartPlay() override;
	AFPSGameMode::AFPSGameMode(const class FObjectInitializer& ObjectInitializer);

	
	
	
};

Hey -

In the explorer path to your project, right click on the .uproject file and select Switch Engine Version to make sure that the project is using the correct version of the engine that you’re building for (4.6.1). If this is set properly then again right click the .uproject and select Generate Visual Studio project files. If you’re still near the beginning of the tutorial and it wouldn’t cost too much work, I would also suggest trying 4.7.3 as well to see if you are still having problems.

Cheers