Failed to load Skysphere when I open a project?

When I open up my project in 4.12.5 I get the following error messages:

In the Engine Content I find these files:

I have tried copying the BP_Sky_Sphere_2 into my scene and adding my scenes light source as the directional light actor but this does not achieve anything. Can anyone please help me to get the original skysphere back?

Works like a charm. Thank you very much!

Close the project and from the Launcher click the down arrow next to your version of the engine in the Library section and select Verify, this should re-download and replace any missing assets from the engine and restore it back.