WPGMaps on "[Plugin: WP Google Maps] Could not save XML file"

Please go to Maps->Settings (left menu in wp-admin) and have a look at the "marker xml dir" and "marker xml url" fields.

Try the following:

Marker XML DIR
{uploads_dir}/wp-google-maps/

Marker XML URL
{uploads_url}/wp-google-maps/

That should now change the DIR and URL dynamically for you.