Why sometime this message appear???

Hi,

I have somethink I need to understand. Why this message appear sometime when I run my program. It doesnt appear allways. But sometime. When Then how can I fix it to evitate because when I comment my connection its works for a while (later its buggs). Even I leave my connection in order or open/close (its works but anytime later its buggs). Thes error message: The connection was not closed. The connection's current state is open.

public Entrada()

{

InitializeComponent();

}

OleDbConnection conn = new OleDbConnection(@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Visa\App_Data\finance.mdb;Persist Security Info=False");

OleDbCommand comm;

string connstr = @"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Visa\App_Data\finance.mdb;Persist Security Info=False";

conn.Open();// the error message point here

OleDbCommand cmd = conn.CreateCommand();

cmd.CommandType = CommandType.Text;

cmd.CommandText = "select * from Lancamento where data_recepcao ='" + dtEntrada.Text + "'";

var param1 = new OleDbParameter("@data_recepcao", OleDbType.VarChar);

param1.Value = dtEntrada.Text;

cmd.ExecuteNonQuery();

DataTable dt = new DataTable();

OleDbDataAdapter da = new OleDbDataAdapter(cmd);

da.Fill(dt);

dgvLancamento.DataSource = dt;

conn.Close();// the error message point here