Angular calling web api net::ERR_FAILED

I have an ASP.NET Web API backend which is called by an AngularJS application and I'm having some problems with calls to the API. I currently get an OK with the first OPTIONS call but the subsequent GET fails without error code and I just see a "Provisional headers are shown" message when viewing in Chrom dev tools.

I thought it maybe a CORS issues as the API and front end work on my local IIS instance without any issue, its just once I use them in a test environment.

I've enabled cors for any requests to try and see if it is something to do with that but same issue persists

var cors = new EnableCorsAttribute("*", "*", "*");
config.EnableCors(cors);