SOLUTION:
Edit the file ‘wp-gpx-maps/js/WP-GPX-Maps.js’ in line 663:
660: if (waypointIcon!='')
661: {
662: icon = L.icon({
663: iconUrl: 'waypointIcon',
664: iconSize: [32, 32], // size of the icon
665: iconAnchor: [16, 16], // point of the icon which will correspond to marker's location
666: });
667: }
And remove de quote:
660: if (waypointIcon!='')
661: {
662: icon = L.icon({
663: iconUrl: waypointIcon,
664: iconSize: [32, 32], // size of the icon
665: iconAnchor: [16, 16], // point of the icon which will correspond to marker's location
666: });
667: }
Regards!