in the google api console, you need to enable the Google Maps API V2
see this page for details:
"Click the Services link from the left-hand menu, then activate the Google Maps API v2 service."
The Pro maps for google extension will not be updated to the newer V3 API. We will no longer be updating the stand alone extension except to fix bugs.
The Pro Maps extension is now part of the Design Extender
in Design extender the PRo maps have been upgraded to use the V3 api. The V2 api in the stand alone extension will continue to work as long as you enable it in the API console.