Error using "Groups" method for IADsUser

I am getting an error (Number=5 Desc =Invalid procedure
call or argument) when I execute the following code. The
error is occurring on the "For each" line:

'START CODE ================================
Dim myDomain As IADsDomain
Dim myUser As IADsUser

Set myDomain = GetObject("WinNT://" & sDomain)
Set myUser = myDomain.GetObject("user", Username)

For Each grp In myUser.Groups
Debug.Print grp.Name
Next
'END CODE ================================

Can anyone tell me why. I am running Windows NT 4.0 SP 6a
.