function CheckZipCode()
	{ 
		var zipCode = document.getElementById('<%=TextBox1.ClientID%>').value; 
		if (zipCode.length != 5) 
		{ 
			alert('Please enter a valid 5 digit postal code!'); 
			return false; // cancel the AJAX request 
		} 
		else 
		{ 
			var fiveDigitCheckRE=/^\d{5}$/ //regular expression for checking a 5 digit number 
			if (zipCode.search(fiveDigitCheckRE) == -1) 
			{ 
				alert("Only digits are allowed!"); return false; 
			} 
		} 
	}