The remote server returned an error: (501) Not Implemented VB - Exchange 2007

Hi ,
I'm using VS 2005 and Exchange 2007. I'm trying to get the attachment which is a jpg image from an email message and save it locally to my HDD.
The code I'm using is the following.

Code:

---

XmlNode.InnerText is a valid path which contains 
https://10.2.5.59/exchange/username/Sent%20Items/TEST.EML/Sunset.jpg
FileNameNode.InnerText is the name of the file which is attached in the email message
 
 
Dim MyCredentialCache As System.Net.CredentialCache 
            Dim bytes() As Byte 
            Dim wcClient As New System.Net.WebClient 
            ServicePointManager.ServerCertificateValidationCallback = New _ 
            RemoteCertificateValidationCallback(AddressOf ValidateCertificate) 
            MyCredentialCache = New System.Net.CredentialCache 
            MyCredentialCache.Add(New System.Uri(_XmlNode.InnerText), _ 
                "NTLM", _ 
                New System.Net.NetworkCredential(UserName, PassWord, Domain) _ 
                ) 
            ' Create the PUT HttpWebRequest object. 
 
            wcClient.Credentials = MyCredentialCache 
 
 
            Dim Str As String 
            Str = _XmlNode.InnerText 
            Dim _ResponseBody() As Byte = wcClient.DownloadData(Str) 
            My.Computer.FileSystem.WriteAllBytes(AttachmentDir & "\" & FileNameNode.InnerText, _ResponseBody, False) 
            MeMe.AttachmentPaths = Me.AttachmentPaths & "=" & AttachmentDir & "\" & FileNameNode.InnerText 
            ' wcClient.DownloadFile(_XmlNode.InnerText, AttachmentDir & "\" & FileNameNode.InnerText) 
            wcClient.Dispose() 
            wcClient = Nothing 
        Catch ex As System.Exception 
            ErrorCode = -1 
            Me.SetErrorMessage(ex.Message) 
            Throw ex 
        End Try

---

After the wcClient.DownloadData(Str) I'm getting an exception
The remote server returned an error: (501) Not Implemented

What is that ?????
How can I overcome with this ?
I have also tried to write wcClient.Downloadfile(url , "c:\test.jpg") but with no success.
Same exception

I have checked the Exchange 2007 and the POP3 is enabled. Should I need to configure anything else ?
What am I missing ?

I have also tried Httpwebrequest and webrequest classes. They return the same error.
Any ideas ?

Thank you