附加信息：尚未为某些必需参数指定值

Question

我已经尝试了一切，这对我来说就是这样：

private void deleteBtn_Click(object sender, EventArgs e)
    {
        string strSQL = "SELECT ficha FROM Empleados WHERE [ID]=@p1 ";

        OleDbCommand cmd = new OleDbCommand(strSQL, conn);
        cmd.Parameters.AddWithValue("@p1", 1);

        conn.Open();
        var oleBytes = (Byte[])cmd.ExecuteScalar();
        conn.Close();
     }