Как Вы получаете IP-адрес от запроса в ASP.NET?

 IpAddress=HttpContext.Current.Request.UserHostAddress;

Используйте этот код:

public static string GetIpAddress()
    {
        return HttpContext.Current != null ? HttpContext.Current.Request.UserHostAddress : "";
    }

Request.ServerVariables["REMOTE_ADDR"]

To access an index or property on C#, you should use [ ] instead of ( )

One method is to use Request object:

protected void Page_Load(object sender, EventArgs e)
{
    lbl1.Text = Request.UserHostAddress;
}