Errors Codes and Missing Texture Preview in material editor.

Using a iMac using latest iOS, when i use the texture editor, I get no preview of the texture just chequer ball, and at the bottom of the node window a separate window opens with the errors listed below. This happens every time, with materials I try to create, and with the stock materials in UE 4.11.1 I have tried removing and reinstalling, any suggestions?

These are the errors;

Error [SM4] …/…/…/Engine/Intermediate/ShaderInE2D3DC843945A34ADA7314A21B4AC790.metal(0): No such executable
Error [SM4] …/…/…/Engine/Intermediate/ShaderIn16B11A664F40C75EBB5944959EC32956.metal(0): No such executable
Error [SM4] …/…/…/Engine/Intermediate/ShaderIn143A933E6F4CA2CB95BCB1A2CAED5B9C.metal(0): No such executable
Error [SM4] …/…/…/Engine/Intermediate/ShaderInEF814F1F184528A720677C925E785D68.metal(0): No such executable
Error [SM4] …/…/…/Engine/Intermediate/ShaderIn55918D2324445EDAC4BE80A111AC48E8.metal(0): No such executable
Error [SM4] …/…/…/Engine/Intermediate/ShaderIn0B6E7DA30546171C36C656A770DF6F02.metal(0): No such executable
Error [SM4] …/…/…/Engine/Intermediate/ShaderIn0C2F2C805D4DF6DB5E7AFD8E4FAE605A.metal(0): No such executable
Error [SM4] …/…/…/Engine/Intermediate/ShaderInCCE5ABFBE240A7A52C6386B7D3AEEAAC.metal(0): No such executable
Error [SM4] …/…/…/Engine/Intermediate/ShaderIn67CD37600A434F056E2C968769E00CCE.metal(0): No such executable
Error [SM4] …/…/…/Engine/Intermediate/ShaderInC7E43C465744B0F8DE25A3A85227AB17.metal(0): No such executable

A future version of UE4 will change our shader compiler’s behaviour to fallback to the slower runtime compiled text shader format but for 4.11 you’ll need to install Xcode because Apple don’t supply their offline ‘metal’ shader compiler with the OS, only the developer tools.

Not that I need to confirm what a staffmember says, but still want to +1 just for the sake of it.
I upgraded my OS to El Capitan and textures were not rendering (in the editor nor in the build). Updating Xcode (to 7.3.1) fixed that problem. (no mac reboot needed). I did restart the editor for changes to take effect.