Same here.
When I try to add a marker, the black overlay comes but nothing else.
jQuery("#wpgamppity_add_marker_go").click(function() {
tb_show('Add a Marker',
"#TB_inline?height=450&width=475&inlineId=wpgmappity_add_marker_dialog",
null);
return false;
});
Add this one instead:
jQuery("#wpgamppity_add_marker_go").click(function(){
jQuery("#wpgmappity_add_marker_dialog").show();
return false;
});