Unable to use the Material Editor under MacOS 10.11.4
Getting error messages of the type: MaterialEditorStats:Error: Error [SM4] …/…/…/Engine/Intermediate/ShaderInCED35FE8F44D2E8B172C009F39FABFB5.metal(0): No such executable
Reverting to UE 4.10 allows me to use Material Editor – but now I can’t use the new Sequencer 
Have you tried rebuilding your project? When I upgraded from 4.10 to 4.11, I had to nuke my intermediate directories by doing a rebuild of my source code.
You must download & fully install Xcode (by opening it and installing its additional components) in order to use UE4 4.11 on Mac because Xcode includes Apple’s ‘metal’ shader compiler tool that we need. In 4.12 we’ll fallback to slower runtime compiled text format shaders, but that change didn’t make it into 4.11.
Many thanks to both respondents.
Installing Xcode (free download from Apple Store) fixed the problem OK 