Hi,
I got the solution for above issue
Instead of using this code.
Response.Write(@"<SCRIPT LANGUAGE=""JavaScript"">alert('" + "Bug created successfully." + "')</SCRIPT>");
Response.Redirect("./ManageDefects.aspx");
Use this one.
ScriptManager.RegisterStartupScript(this, typeof(string), "redirect", "alert('message goes here'); window.location='" + Request.ApplicationPath + "/foldername/pagename.aspx';", true);