C#SqlDataReader行/列没有数据

我使用sql Server Compact Edition 4.0(VS2012内置)的sql DataReader有问题.

String connString = "Data source=C:\\..(Path HerE)..\\VacationsDB.sdf";
sqlCeConnection conn = new sqlCeConnection(connString);
String strsql = "SELECT * FROM Vacation WHERE VacationNo = @val";

using (sqlCeCommand cmd = new sqlCeCommand(strsql,conn))
{
    //read search value from from text field
    cmd.Parameters.AddWithValue("@val",vacationno_txt.Text);
    conn.open();

    sqlCeDataReader reader = cmd.ExecuteReader();
    fname_txt.Text = reader.GetString(0);
    mname_txt.Text = reader.GetString(1);
    /*
     * .. snip
     */
    vacationno_txt.Text = reader.GetString(11);
    conn.Close();
}

我一直收到错误：
“InvalidoperationException未处理.行/列没有数据.”并且错误指向
    fname_txt.Text = reader.GetString(0);

但实际上有数据,因为带有所有代码的“提交”按钮正在运行,我已经在数据库表中检查了它.

有小费吗？谢谢.