how can i insert js block from server on master page?

i have a button click event inside updatepanel in a content using master page..
js alert not working on master page 
Response.Write("<script language=javascript>alert('" + sMassege + "');</script>"); // or string s = "<script language=javascript>alert('" + sMassege + "');</script>"; Page.ClientScript.RegisterStartupScript(this.GetType(), "onload", s); how can i raise js from server on master page? 

i am getting this error
Unhandled exception at line 885, column 13 in http://localhost:49721/ScriptResource.axd?d=snkoblAKUnL886ugmAh4-C8porVSqWQKtBVVBVutZ12grGGZ9Od9RIurOde8tzHGfcYKZeFaF2WgqHvKgqJSfiQDt5aNi1VayU4g7Qj6K7k1uNUCp0k1cXYwe1gNedP5zIQcJhlGguwvroGw3FETOGqt0LChBfgKHO1JhPb8aHXX9lkQAEJCuBgJbTWLkfHe0&t=ffffffffb53e74b8
0x800a139e - JavaScript runtime err ...