How to use a combo box to select email address and password for creating emails

Hoping someone can help. We have switched from Outlook to Gmail and I need my Access Database to create emails that are sent out at the press of a button. This used to work for Outlook, and I have adapted the code for Gmail and it works perfectly, except that if I don't want to hardcode the email username and password, it doesn't seem to want to pick it up from a combobox on the main form? I have checked the combo boxes work with a text box and they work fine. I just get the error below. Any Ideas?

Private Sub Email_Allocation_List_Click()

Dim newMail As CDO.Message
Dim mailConfiguration As CDO.Configuration
Dim fields As Variant
Dim msConfigURL As String

On Error GoTo errHandle

Set newMail = New CDO.Message
Set mailConfiguration = New CDO.Configuration

mailConfiguration.Load -1

Set fields = mailConfiguration.fields

With newMail
    .Subject = "subject"
    .From = [Forms]![Main form]![EmailAddress].Column(1)
    .To = "email address"
    .CC = "email address"
    .BCC = ""
    .TextBody = "Hello, "& vbNewLine & vbNewLine & _
      "Please find attached todays list of lines to be allocated."& _
       vbNewLine & vbNewLine & "Kind Regards."& vbNewLine & vbNewLine & "Carly"
    .AddAttachment "file location"
End With

msConfigURL = "http://schemas.microsoft.com/cdo/configuration"

With fields
    .Item(msConfigURL & "/smtpusessl") = True
    .Item(msConfigURL & "/smtpauthenticate") = 1

    .Item(msConfigURL & "/smtpserver") = "smtp.gmail.com"
    .Item(msConfigURL & "/smtpserverport") = 465
    .Item(msConfigURL & "/sendusing") = 2

    .Item(msConfigURL & "/sendusername") = [Forms]![Main form]![EmailAddress].Column(1)
    .Item(msConfigURL & "/sendpassword") = [Forms]![Main form]![EmailAddress].Column(2)

    .Update

End With

newMail.Configuration = mailConfiguration
newMail.Send

MsgBox "E-Mail has been sent", vbInformation

exit_line:
'// Release object memory
Set newMail = Nothing
Set mailConfiguration = Nothing

Exit Sub

errHandle:

MsgBox "Error: "& Err.Description, vbInformation

GoTo exit_line

End Sub