Update to Store Locator v2! Important!
It is mandatory that you update to v2 of the WordPress Store Locator, because it uses Google Maps API v3.
Older Store Locator versions use Google Maps API v2, which is being shut off soon.
Older Versions Will Not Geocode Your Locations Anymore
In fact, Google Geocoding API v2 seems to already be off. No further questions concerning geocoding errors will be answered for those of you using old versions before Store Locator v2 (geocoding: giving your locations latitude & longitude coordinates).
Just like keeping WordPress up-to-date, keeping your Store Locator up-to-date is crucial, due to changes to external services/APIs such as Google Maps.
Announced This Twice So Far, Don’t Hesitate — Update!