Signup new member gives the WP_Error for Google Maps

Google maps plugin works correctly for members already subscribed; the map shows nicely in their profile.

However, when a new member tries to subscribe following error is displayed:

Fatal error: Cannot use object of type WP_Error as array in [mydomain]/public_html/wp-content/plugins/wpmu_dev_maps_plugin/lib/class_agm_map_model.php on line 665

which is the line
$json = json_decode($result['body']);
in the fuction geocode_address($address){ } .

All signup information after address-field isn't saved (account does register).

Information in address-field is findable for maps in already signed-up members...

I saw this is somewhat a 'known' error with for example the Membership plugin (not installed on my wp mu buddypress site)?

Any idea?