error in creating a custom control hello world

[yogeshtiwarijbp]

iam making a custom control in a website in asp.net2005 . The code is as follows

namespace Wintellect
{
public class Hello :System.Web.UI.Control
protected override void Render(HtmlTextWriter writer)
{
writer.Write("Hello, World");
}
}
}

and in hello.aspx page i write

<%@ Register TagPrefix="win" namespace="Wintellect" %>
and inside form tag
<win:Hello RunAt="server" />

the following error occurs:
Error 1 Element 'Hello' is not a known element. This can occur if there is a compilation error in the Web site.E:\websites\customdemo\Hello.aspx

Error 2 Unknown server tag 'win:Hello'.

plz. help yogesh