HI,
To display a message box in asp.net you must use javascript in your html view of your form.Code is as followes.
In head teg of HTML View of your Web Form write the following code
<head>
<Script language="JavaScript">
function showMsg()
{
alert("Your message Here");
}
</Script>
</head>
To Call this function write the following code in ur Page_Load event code in (C#)
UrControlid.Attribute.Add("OnClick","return showMsg();");
I hope It will work.
Unsolved 
