want to insert data od gridview to database, got an error ->"Transaction no has already been decleared" Plz help me with this. Thanx

String query = "insert into Account_Credit(Transaction_No,Account_No,Amount_Credit,Credit_Date,Total_Amount_Credit)values(@Transaction_No,@Account_No,@Amount_Credit,@Credit_Date,@Total_Amount_Credit)";
                cmd = new SqlCommand(query, cn);
               cmd.Prepare();

               int i = dataGridView1.CurrentRow.Index;
               cmd.Parameters.AddWithValue("@Account_No", dataGridView1.Rows[i].Cells[0].Value);
               for (i = 0; i <= dataGridView1.Rows.Count - 1; i++)
               {


                   cmd.Parameters.AddWithValue("@Transaction_No", dataGridView1.Rows[i].Cells[1].Value);
                   cmd.Parameters.AddWithValue("@Amount_Credit", dataGridView1.Rows[i].Cells[2].Value);
                   cmd.Parameters.AddWithValue("@Credit_Date", dataGridView1.Rows[i].Cells[3].Value);
                   cmd.Parameters.AddWithValue("@Total_Amount_Credit", dataGridView1.Rows[i].Cells[4].Value);
                   cn.Open();


                   cmd.ExecuteNonQuery();
                   cn.Close();
               }