Extension is not working properly

The 'Tooltip description' box in the 'add new marker' map isn't showing. We cannot add markers to our map and no descriptions, they don't show on the map at all. We have just an empty map on our site, without markers. We get this warning:

Warning: Invalid argument supplied for foreach() in /public/sites/http://www.magnesiumcentrum.com/components/com_linkymap/helpers/linkymap.php on line 242