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.