"An error occurred while trying to fetch data from your sharepoint site" + "The status is 'OK'"
No it's not ok!
Looking at different blog posts several suggestions were provided: different build version, IIS binding issues, and so on.
BUT what fixed it in my case was these steps (suggested by JacobEgholm):
- In IIS select authentication for the web app that causes you headaches
- Select Windows Authentication
- Select Advanced settings and turn off Extended protection