The show multiple option will only be available if you are using a recordset, If you are using a recordset, it will on,y use the first record in the recordset, checking the show multiple option tells it to loop through the entire recordset.
Some addresses the Maps API simply cannot geocode, in these cases you need to use latitude and longitude coordinates.
To find the latitude and longitude, go to maps.google.com and search for your address. When the address is found, enter the following code in the address bar:
This will pop up an alert box with the latitude and longitude for your address.