IntelliJ refuses to recognise groovy script in one module, others are fine

I have groovy 2.4.3 installed and I'm developing a project with Jenkins groovy scripts. I have about 10 groovy scripts in 5 project modules.

In one module, the 2 groovy files are full of issues - it doesn't compile since groovy.c says its unable to resolve class libraries or classes, and the groovy functions are all underlined as 'symbol unresolved'.

Why this one module? It's not the root module, but AFAICT it's configured the same as the other 2 additional modules where groovy is handled fine.