Google Maps Api v3 custom InfoWindow - "google is not defined" error

trying to create custom infowindows in my application that is based on google maps.

next example is one of my base points for development:

http://gmaps-samples-v3.googlecode.com/svn/trunk/infowindow_custom/infowindow-custom.html

problem is that whatever i use this or some other example, in forefox's firebug i'm getting error

google is not defined
InfoBox.prototype = new google.maps.OverlayView();

can you help me how to solve this, i can not continue my work without custom infowindows.....

How do I fix uncaught ReferenceError Google is not defined?

Uncaught ReferenceError: google is not defined error will be gone when removed the async defer from the map API script tag. Save this answer.

What is InfoWindow in Google Map?

An InfoWindow displays content (usually text or images) in a popup window above the map, at a given location. The info window has a content area and a tapered stem. The tip of the stem is attached to a specified location on the map. Info windows appear as a Dialog to screen readers.

my mistake - i did not include properly google map api library - i included infobox.js before http://maps.google.com/maps/api/js?sensor=false