function checkRequiredFields() {
		
	var message = new Array();
	var errorLevel;
	errorLevel = 0;
	
	message[0]  = "";
   	message[1] = "Inserire lo username";
	message[2] = "Inserire la password";

	if ((errorLevel == 0) && ((document.FormN.username.value.length == 0) || isSpace(document.FormN.username.value))) {
		errorLevel = 1;	
		document.FormN.username.focus();
	}
	if ((errorLevel == 0) && ((document.FormN.password.value.length == 0) || isSpace(document.FormN.password.value))) {
		errorLevel = 2;	
		document.FormN.password.focus();
	}

	if (errorLevel > 0 ) { 
		alert(message[errorLevel]); 
		return false;
	}

}