by the way you better writw the connection string in webconfig ofcourse as soon as you dont want to get trouble

here it i body disconnected way SqlConnection sqlcon = new SqlConnection("server=.;database=tabakus;Trusted_connection=true"); SqlDataAdapter da = new SqlDataAdapter("select * from musteri",sqlcon); DataTable dt = new DataTable(); da.Fill(dt); GridView1.DataSource = dt; GridView1.DataBind();

I see here codebehind but what if on the design side button name is not "topic" what if the button name was "button1" thats what i am try to tell and its very possiable if you copy and past the design code

if you copy and past the code from another page visual studio may change the name of the button check the the ButtonID if its correct with the code