Posting picture with sdk facebook in vb.net

I'm trying to post a picture with sdk facebook

fb = New FacebookClient(_accessToken) 'Get access
    Dim companyLogo As Image

    Try

        fb.Post("me/photos", New Dictionary(Of String, Object) From { _
        {"message", TextBox3.Text}, {"photos", PictureBox8.Image} _
        })

        Dim imgLocation As String = TextBoxX1.Text
        Using imgStream As System.IO.Stream = IO.File.OpenRead(imgLocation)
            companyLogo = Image.FromStream(imgStream)
        End Using
        PictureBox8.Image = companyLogo

        MessageBox.Show("Message posted successfully")

        Exit Sub

where is the problem ?

thank you :)