运行一下代码，系统老提示：操作必须使用一个可更新的查询。 为什么？
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim ConnString As String
        Dim strSql As String
        Dim Conn As New OleDbConnection
        ConnString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source="
        ConnString += Server.MapPath("22.mdb")
        Conn.ConnectionString = ConnString
        Conn.Open()
        Dim cmd As New OleDbCommand
        Dim lngCount As Long
        strSql = " select * from mima where 学号='" & xuehao.Text & "'"
        cmd.Connection = Conn
        cmd.CommandText = strSql
        lngCount = cmd.ExecuteScalar()
        Try
            If lngCount = 0 Then

                strSql = " insert into mima values( '" & xuehao.Text & "','" & xingming.Text & "','" & mima.Text & "','" & dianhua.Text & "','" & youxiang.Text & "','" & dizhi.Text & " ') "

                cmd.Connection = Conn
                cmd.CommandText = strSql
                cmd.ExecuteNonQuery()
                Response.Write("恭喜")
            Else
                Response.Write("对不起，你的用户名已经有人使用")
                Response.Write("请更换其它名称再进行注册。")
            End If
        Catch Err As Exception
            Response.Write(Err.Message)
        End Try

        cmd.Dispose()
        Conn.Close()
    End Sub

End Class