Where have you placed the plug-in in your project folder?
It is in C:\Program Files\Epic Games\UE_4.11\Engine\Plugins.
And did you delete all these folders before re-creating the solution file - and does the file in question have any UE-types like i mentioned above?
Yes, I think so. For example, there is no Intermediate or Binaries folders before project files generating. And the plugin “OptitrackNatNet” was also defined in the Build.cs file as shown below.
using UnrealBuildTool;
public class OffAxisWindow : ModuleRules
{
public OffAxisWindow(TargetInfo Target)
{
PublicDependencyModuleNames.AddRange(new string] { “Core”, “CoreUObject”, “Engine”, “InputCore”, “HeadMountedDisplay”, “OptitrackNatNet”});
PrivateDependencyModuleNames.AddRange(new string] { “Slate”, “SlateCore” });
PublicIncludePaths.AddRange(new string] { “OptitrackNatNet/Public”, “OptitrackNatNet/Classes” });
}
}