in the webassist/google_javascript/wagmp_map_1.php file edit the following line:
function WAMapPoint(theMarker, theAddress, theIcon, point, map) {
to:
function WAMapPoint(theMarker, theAddress, theIcon, theInfoWindow, point, map) {
and this line:
return WAMapPoint(this.markers[x],this.addresses[x],this.icons[ x], this.points[x], this.obj);
to:
return WAMapPoint(this.markers[x],this.addresses[x],this.icons[x], this.infowindows[x], this.points[x], this.obj);
I think you may have an older version of Design Extender that is causing the incorrect code, The current version is 1.1.0. if you have a previous version, make sure to uninstall it from the extension manager before installing the newer one.