pois open popup

hello,

the popup will not open if all the layers are active, why?
if active layers 2 is ok, but 3 does not work ??!

<script src="OpenLayers.js"></script>
		<script type="text/javascript" src="OpenStreetMap.js"></script>
        
		<script type="text/javascript">
            var map;
			var lon =9.19;
			var lat =45.46;
			var zoom =10;
			
            function init(){
                map = new OpenLayers.Map("map", {
				controls: [
                new OpenLayers.Control.Navigation(),
                new OpenLayers.Control.LayerSwitcher()
				]
			});
			
			layerMapnik = new OpenLayers.Layer.OSM.Mapnik("Mapnik");
            layerMapnik.setOpacity(0.4);
            map.addLayer(layerMapnik); 
			
			var newLayer = new OpenLayers.Layer.OSM("Mappa locale", "tiles/${z}/${x}/${y}.png", {numZoomLevels: 19, alpha: true, isBaseLayer: false});
            map.addLayer(newLayer);

				
		// Layer Sedi
                var layer_sedi = new OpenLayers.Layer.Vector("Sedi libere", {
                    strategies: [new OpenLayers.Strategy.BBOX({resFactor: 1.1})],
                    protocol: new OpenLayers.Protocol.HTTP({
                        url: "./geco_sedi.txt",
                        format: new OpenLayers.Format.Text()
                    })
                });
                map.addLayer(layer_sedi); 

				
                // Interaction; not needed for initial display.
                selectControl = new OpenLayers.Control.SelectFeature(layer_sedi);
                map.addControl(selectControl);
                selectControl.activate();
                layer_sedi.events.on({
                    'featureselected': onFeatureSelect,
                    'featureunselected': onFeatureUnselect
                });
		// End Layer Sedi
				
			
		// Layer Stazionamenti
                var layer_stazionamenti = new OpenLayers.Layer.Vector("Stazionamenti liberi", {
                    strategies: [new OpenLayers.Strategy.BBOX({resFactor: 1.1})],
                    protocol: new OpenLayers.Protocol.HTTP({
                        url: "./geco_stazionamenti.txt",
                        format: new OpenLayers.Format.Text()
                    })
                });          
                map.addLayer(layer_stazionamenti); 

                // Interaction; not needed for initial display.
                selectControl = new OpenLayers.Control.SelectFeature(layer_stazionamenti);
                map.addControl(selectControl);
                selectControl.activate();
                layer_stazionamenti.events.on({
                    'featureselected': onFeatureSelect,
                    'featureunselected': onFeatureUnselect
                });
		// End Layer Stazionamenti
				
				
				// Layer Mezzi Disponibili
				var layer_mezzidisponibili = new OpenLayers.Layer.Vector("Mezzi disponibili", {
                    strategies: [new OpenLayers.Strategy.BBOX({resFactor: 1.1})],
                    protocol: new OpenLayers.Protocol.HTTP({
                        url: "./geco_mezzidisponibili.txt",
                        format: new OpenLayers.Format.Text()
                    })
                });
				map.addLayer(layer_mezzidisponibili);
				
			
				// Interaction; not needed for initial display.
                selectControl = new OpenLayers.Control.SelectFeature(layer_mezzidisponibili);
                map.addControl(selectControl);
                selectControl.activate();
                layer_mezzidisponibili.events.on({
                    'featureselected': onFeatureSelect,
                    'featureunselected': onFeatureUnselect
                });
				// End Layer Mezzi Disponibili
				
				
				
				if( ! map.getCenter() ){
					var lonLat = new OpenLayers.LonLat(lon, lat).transform(new OpenLayers.Projection("EPSG:4326"), map.getProjectionObject());
					map.setCenter (lonLat, zoom);
				}
            }
             

            // Needed only for interaction, not for the display.
            function onPopupClose(evt) {
                // 'this' is the popup.
                var feature = this.feature;
                if (feature.layer) { // The feature is not destroyed
                    selectControl.unselect(feature);
                } else { // After "moveend" or "refresh" events on POIs layer all 
                         //     features have been destroyed by the Strategy.BBOX
                    this.destroy();
                }
            }
            function onFeatureSelect(evt) {
                feature = evt.feature;
                popup = new OpenLayers.Popup.FramedCloud("featurePopup",
                                         feature.geometry.getBounds().getCenterLonLat(),
                                         new OpenLayers.Size(100,100),
                                         "<h2>"+feature.attributes.title + "</h2>" +
                                         feature.attributes.description,
                                         null, true, onPopupClose);
                feature.popup = popup;
                popup.feature = feature;
                map.addPopup(popup, true);
            }
            function onFeatureUnselect(evt) {
                feature = evt.feature;
                if (feature.popup) {
                    popup.feature = null;
                    map.removePopup(feature.popup);
                    feature.popup.destroy();
                    feature.popup = null;
                }
            }
			
		
        </script>