When you’re in ADFS v2.0 and you are trying to update the metadata of a CP or RP, you sometimes get the “An error occurred during an attempt to read the federation metadata” message.
A useful trick is to open a browser and navigate to the URL of the site whose metadata you are attempting to update. If you get any certificate errors, fix them first. ADFS does not like certificate errors. Everything has to be squeaky clean!