function checkEmpty()
{
	if (document.getElementById('Nav_txtEmail').value=='' || document.getElementById('Nav_txtEmail').value==null)
	{
		alert("Please enter your email address to login.");
		return false;	
	}
	else
		return true;
}
function enterPress(e)
{
	var key = window.event ? e.keyCode : e.which;
	if (key == 13)
	{
		return checkEmpty();
	}
}