When we click a Linkbutton or Image button it must open a pop up window.below is the code for that you can place in any of the button events
string s = "javascript:pop_window=window.open('popup.aspx',
'pop_window','width=400,height=400,top=50,left=100');
pop_window.focus()";
Page.ClientScript.RegisterClientScriptBlock
(this.GetType(), "s", s, true);
Bharath Radhekrishna 
super posts,
it is very useful for me..
thanQ
praveen
thanx..
i did it this way
ScriptManager.RegisterStartupScript(this.Page, this.GetType(), “Message-ABC”, (‘”No project data is available to view this Screen.Please contact the administrator at support” + “@” + “xyz.com!!!” ‘), true);