1.8t fault code

Hello. I did this conversion years ago and was all good. Life and family have taken over in recent years and I haven't touched the Golf in a few years. 
I started it Saturday fine. Now won't start. It's like an immobiliser is blocking it. But the immobiliser was removed from the ECU years back. And didn't stop it stating Saturday. When I plugged it in I get fault 18058 "missing message from instrument cluster". I'm almost certain that fault never used to show. And the fault stays when I clear codes even without cranking the car again. 
I just need an idea of which direction to be looking in?

Cheers, Skipp