Change the query like below
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)";
int i = dataGridView1.CurrentRow.Index;
for (i = 0; i <= dataGridView1.Rows.Count - 1; i++)
{
cmd = new SqlCommand(query, cn);
cmd.Prepare();
cmd.Parameters.AddWithValue("@Account_No", dataGridView1.Rows[i].Cells[0].Value);
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();
}