Raja,
Please refer to the codes below:
var OnMapCreated = function(map) {
// MarkerOverlay is the id for your SimpleMarkerOverlay
var markerOverlay = map.getLayer('MarkerOverlay');
for (var i in markerOverlay.markers) {
var marker = markerOverlay.markers[i];
marker.events.register('click', marker, function(evt) {
var id = this.id;
// Add your popup like the code below:
//var popup = new OpenLayers.Popup.FramedCloud();
//map.addPopup(popup);
});
}
}
If you still have any questions about it please feel free to let us know.
Thanks,
Khalil