Error with HTTP Get


I have experience dealing with http request, but yesterday i try a GET request for a new app that i’m working.
The server gave me STATUS CODE: 200 OK which great but in the console i found this error:
XMLHttpRequest cannot load: No ‘Access-Control-Allow-Origin’ header is present on the requested resource. Origin ‘http://localhost:8100’ is therefore not allowed access.
I know about CORS Headers and the fact that in my server i have to set access to call my methods.
The Question is why i get an STATUS CODE 200 and also an ERROR which dont let me access the information that i wanted.