problem in text change event of combobox

I have two combobox  comboboxP (fetch products name) and comboboxB (fetch  Batchno)  . I put code in comboboxP textchanged event to fetch data in comboboxB and other textboxes . when i select any value in comboboxB its related textboxes and comboboxP also should b filled with related values.this is my code for comboboxP in which you can see comboboxB is getting value on changing comboboxP's text.

 

private void comboProname_TextChanged(object sender, EventArgs e)
{
cmd = new SqlCommand("select P_batchno,P_min_stk,P_max_stk,P_vat from PRO where P_name='" + comboProname.Text + "'", conn);
  conn.Open();
SqlDataReader reader = cmd.ExecuteReader();
AutoCompleteStringCollection MyCollection7 = new AutoCompleteStringCollection();
AutoCompleteStringCollection MyCollection9 = new AutoCompleteStringCollection();
AutoCompleteStringCollection MyCollection10 = new AutoCompleteStringCollection();
AutoCompleteStringCollection MyCollection11 = new AutoCompleteStringCollection();
while (reader.Read())
{
MyCollection7.Add(reader["P_batchno"].ToString());
MyCollection9.Add(reader["P_max_stk"].ToString());
MyCollection10.Add(reader["P_min_stk"].ToString());
MyCollection11.Add(reader["P_vat"].ToString());

comboBthNo.Items.Add(reader["P_batchno"].ToString());

tbMaxStk.Text = (reader["P_max_stk"].ToString());
tbMinstk.Text = (reader["P_min_stk"].ToString());
tbVAT.Text = (reader["P_vat"].ToString());
}
comboBthNo.AutoCompleteCustomSource = MyCollection7;
tbMaxStk.AutoCompleteCustomSource = MyCollection9;
tbMinstk.AutoCompleteCustomSource = MyCollection10;
tbVAT.AutoCompleteCustomSource = MyCollection11;

conn.Close();
} 

// now see code for comboboxB's text change in dis comboboxP's value is changed

 

private void comboBthNo_TextChanged(object sender, EventArgs e)
{
cmd = new SqlCommand("SELECT P_name,P_pack,P_comp,P_rate,P_mrp from PRO where P_batchno='" + comboBthNo.Text + "'", conn);
conn.Open();
SqlDataReader reader = cmd.ExecuteReader();
AutoCompleteStringCollection MyCollection5 = new AutoCompleteStringCollection();
AutoCompleteStringCollection MyCollection6 = new AutoCompleteStringCollection();
AutoCompleteStringCollection MyCollection8 = new AutoCompleteStringCollection();
AutoCompleteStringCollection MyCollection12 = new AutoCompleteStringCollection();
AutoCompleteStringCollection MyCollection13 = new AutoCompleteStringCollection();

while (reader.Read())
{
MyCollection5.Add(reader["P_name"].ToString());
MyCollection6.Add(reader["P_comp"].ToString());
MyCollection8.Add(reader["P_pack"].ToString());
MyCollection12.Add(reader["P_rate"].ToString());
MyCollection13.Add(reader["P_mrp"].ToString());

comboProname.Text = reader["P_name"].ToString();
tbPAck.Text = (reader["P_pack"].ToString());
tbCmpName.Text = (reader["P_comp"].ToString());
tbRate.Text = (reader["P_rate"].ToString());
tbMrp.Text = (reader["P_mrp"].ToString());
}
comboProname.AutoCompleteCustomSource = MyCollection5;
tbPAck.AutoCompleteCustomSource = MyCollection6;
tbCmpName.AutoCompleteCustomSource = MyCollection8;
tbRate.AutoCompleteCustomSource = MyCollection12;
tbMrp.AutoCompleteCustomSource = MyCollection13;

conn.Close();
} 

 

 it is trowing exception another reader is already attached to it is open... someting like this .. help me in fixing it