vb.net编写邮件发送程序的问题请教！

最近编写一个邮件发送程序，点发送时出下以下错误：未能访问"CDO.Message"对象
主要代码：
Public Class FrmSendMail
Inherits System.Windows.Forms.Form
Dim message As New MailMessage()
'定义一个新的邮件消息
Dim sendTo As String
'定义存取发送目的地址
Dim sendFrom As String
'定义存取发送原址
Dim Subject As String
'定义邮件标题
Dim Attachs As MailAttachment
'定义邮件附件，注意，在这里一次只能添加一个附件
Dim proity As MailPriority
'定义邮件发送优先级别
。。。。。。。。。。。。。。。。。。
Private Sub Button1_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles Button1.Click
Try
Me.ComboBox1.SelectedIndex = 0
sendto = Me.TextBox1.Text
sendfrom = Me.TextBox2.Text
If sendto = "" Then
MessageBox.Show("没有邮件目的地址，请重新输入，" & _
"并注意格式的正确性。", "错误", _
MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
Exit Sub
End If
'获取并判断目的地址是否为空
message.To = sendto
message.From = sendfrom
'设置邮件的发送目的地址和原址
If Me.RadioButton1.Checked = True Then
message.BodyFormat = MailFormat.Text
End If
If Me.RadioButton2.Checked = True Then
message.BodyFormat = MailFormat.Text
End If
'选择邮件发送的格式
message.BodyEncoding = System.Text.Encoding.UTF8
'选择邮件发送的文本编码
subject = Me.TextBox3.Text
Dim result As DialogResult
If subject = "" Then
result = MessageBox.Show("该封邮件没有添加标题，不要标题吗？", _
"提示", MessageBoxButtons.YesNo, MessageBoxIcon.Exclamation)
End If
'判断该邮件是否具有标题
If result = DialogResult.No Then Exit Sub
'如果选择要添加标题，则退出过程等待添加标题
message.Subject = subject
'设置邮件发送标题
message.Body = Me.RichTextBox1.Text
'获取邮件发送的内容
If Me.TextBox4.Text = "" Then
Else
attachs = New MailAttachment(Me.TextBox4.Text)
message.Attachments.Add(attachs)
'判断是否具有附件，如果有则连带附件发送
End If
If Me.TextBox5.Text = "" Then
Else
message.Cc = Me.TextBox5.Text
End If
'判断是否有抄送地址
SmtpMail.SmtpServer = "218.*.**.**"
Try
SmtpMail.Send(message)
Catch
MessageBox.Show(Err.Description, "错误", MessageBoxButtons.OK, MessageBoxIcon.Error)
Exit Sub
End Try
'发送邮件
Catch
MessageBox.Show("邮件没有发送成功！原因是：" & Err.Description, _
"错误", MessageBoxButtons.OK, MessageBoxIcon.Error)
'获取可能发生意外的错误并通知用户
Select Case Me.ComboBox1.SelectedIndex
Case 0
proity = MailPriority.Normal
Case 1
proity = MailPriority.High
Case 2
proity = MailPriority.Low
End Select
message.Priority = proity
'选择并设置邮件发送的优先级
MessageBox.Show("邮件已经成功发送完毕。", "提示", _
MessageBoxButtons.OK, MessageBoxIcon.Information)
'
End Try
End Sub
请问是什么问题？谢谢各位指教