ExecuteScalar

private void buttonLogin_Click(object sender, EventArgs e)
{
SqlConnection conn = new SqlConnection();
conn.ConnectionString = "Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirecto ry|\PEService.mdf;Integrated Security=True;User Instance=True";
conn.Open();
string strSQL = "Select Count(*) as ctr From Cust Where Email=" + textBoxEmail + "and Passwd=" + textBoxPW;

SqlCommand cmd = new SqlCommand(strSQL,conn);
int ctr=(int)cmd.ExecuteScalar();
if (ctr == 1)
MessageBox.Show("Correct");
else
MessageBox.Show("Wrong");
conn.Close();
}

i have this code for my login form. when i remove conn.Open(); in the code
it says... ExecuteScalar requires an open and available Connection. The connection's current state is closed.

and when i put conn.Open();
it says... An attempt to attach an auto-named database for file C:... failed. A database with the same name exists, or specified file cannot be opened, or it is located on UNC share.

what is the problem?