What exactly do you mean by “using the service to rebuild…”? When I create a new project and add a code class based on actor, I can then build the project solution in XCode pressing the play button successfully. Can you provide any additional information on what exactly you’re doing after creating a new blank C++ project?
The bug is far less serious than it looks - the project is generated correctly. GenerateProjectFiles script prints the error that it couldn’t build UnrealBuildTool, but then it carries on and uses UnrealBuildTool that we distribute with the engine. The error will be gone in 4.13.
This post was specifically related to Services->Generate XCode Project failing with the error provided by rotwang. If you’re having issue packaging your project, it may be best to create a new post with as much detailed information as possible.