كيفيفة اضافة ملف مرفق للميل

Error in attaching a file with the email in ASP.Net?

1- I decleare a public variable of type MailAttachment with name objMailAttachment.

2- I add a file field (HTML Control) to the form, named it fileAttach.

3- I write this code in send button Sub:

Dim mail As New MailMessage

mail.From = "itcenteronline@yahoo.com"

mail.To = txtmail.Text

mail.Subject = txtSubject.Text

mail.Body = txtBody.Text

If fileAttach.PostedFile.ContentLength <> 0 Then

objMailAttachment = New MailAttachment(fileAttach.PostedFile.FileName)

mail.Attachments.Add(objMailAttachment)

End If

SmtpMail.Send(mail)

So what is wrong?????????