Manual SQl Dont Work Correctly

Hello All Prg's
I need your help,
I use Database SQL server Express with C#
when I entred some data into DB by clciking on the table in server Explorer in Visual Studio 2005 IDE,
and then I make SQL in the code
as:
if (e.KeyCode == Keys.Return)
{
bool res;
int OldPlayerId = 0;
string ConnectionStr = Program.Member_Connect;
string sqlQuery = "select Player_ID from Player where Player_Code = '" + textBox1.Text + "'";
SqlConnection Sql_connection = new SqlConnection(ConnectionStr);
Sql_connection.Open();
SqlCommand command = new SqlCommand(sqlQuery, Sql_connection);
SqlDataReader dataReader = command.ExecuteReader();
if (dataReader.HasRows)
{
if (dataReader.Read())
OldPlayerId = dataReader.GetInt32(0);
else
MessageBox.Show("rtet");
}
else
{
res = false;
}
comboBox2.SelectedValue = textBox1.Text;
command.Dispose();
Sql_connection.Close();
Sql_connection.Dispose();
comboBox1.SelectedValue = OldPlayerId;
}
it work correctly on the old data that I entred them manualy, but when I enter new data from my project, this query don't give correct value, it still work correctly on old data,

I tried to take same data by combobox connected to view that contain same sql ,it work always.
but I need manualy Sql.
Please help me , I am very lating to delever my project...
please help me
thank you very mush