Map was broke in version 1.3.8 The map image would not show.
Try version 1.3.9, it should be fixed. Sorry for the inconvenience.
http://wordpress.org/extend/plugins/visitor-maps/changelog/
1.3.9
* (16 Apr 2010) - Fixed missing map image in version 1.3.8
1.3.8
* (16 Apr 2010) - Split code into smaller files for better memory
performance.
* Added PHP Memory Limit increase code in GeoLiteCity data
updater/installer.
* Added Belorussian (be_BY) - Translated by Marcis