function check_housenumber() {

	var b_housenumber = document.forms["registerform"].b_housenumber.value;
	var b_streetname = document.forms["registerform"].b_streetname.value;
//	var b_additional = document.forms["registerform"].b_additional.value;
	
	var s_housenumber = document.forms["registerform"].s_housenumber.value;
	var s_streetname = document.forms["registerform"].s_streetname.value;
//	var s_additional = document.forms["registerform"].s_additional.value;

	var ship2diff = document.getElementById('ship2diff');

	if ((b_housenumber != "" && isNaN(b_housenumber)) || (s_housenumber != "" && isNaN(s_housenumber))) { 
		alert(alert_housenumber); 
		return false;
	}

//	if (b_housenumber != "" && (b_streetname=="" || b_additional=="")) { 
	if (b_housenumber == "" || b_streetname == "") {
		alert(alert_housenumber2);
		return false;
	}

//    if (s_housenumber != "" && (s_streetname=="" || s_additional=="")) {
	  if (ship2diff.checked && (s_housenumber == "" || s_streetname == "")) {
        alert(alert_housenumber2);
        return false;
    }

	return true;
}