function clearError(sender, error_tag_name)
{
	if(sender.value != '') document.getElementById(error_tag_name).innerHTML = '';
}



function is_valid_email(email)
{
	return /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/.test(email);
}