This is probably due because you have send too many geocode request in a certain time. Google allow 2500 geocode per 24h per IP, and is not advised to send too many request per second.
On some shared hosting (like ovh), the same ip is used for many site, and your quota is used by another site on the server.
Using an API key, will not help, because Google API key is only for displaying maps.
The Geocode itself is always done with the bigger accuracy as possible. Geocode Factory always uses theses coordinates. But there is 2 solution to reduce this accuracy: