Please download the latest version v1.5.11 http://www.kksou.com/php-gtk2/Joomla-Gadgets/googleMaps-plugin.php
The googleMaps plugin is now W3C XHTML 1.0 Transitional.
: Please also make use you read the following: Making the plugin W3C XHTML 1.0 Transitional
Please test if this is W3C XHTML 1.0 Strict.
If it's not, please email me a copy of a joomla template that is XHTML 1.0 Strict, and I will try to come out with a XHTML 1.0 Strict version of googleMap.
All my joomla templates are only XHTML 1.0 Transitional. Even the default Joomla 1.5 templates that you download from joomla.org are only XHTML 1.0 Transitional. They are not XHTML 1.0 Strict.