Help with ADO (not .NET) code for querying MAPI folder

I can't get the following subroutine to work. It's meant to query a MAPI public folder and return the first record. Can anyone tell me where I'm going wrong? It returns the error message: "Run-time error ‘-2147217900 (80040e19)’:" when it tries to open the recordset at the end of the routine.

Also, can you please explain why the second version of 'strUrlFolder (commented out) doesn't work?

Thanks

(PS - the code includes a custom function called Quote that simply adds quotes around a string value.)

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Sub ADO_QueryMAPIFolder()
    Dim cnn As ADODB.Connection
    Dim rst As ADODB.Recordset
    Dim strUrlFolder As String
    Dim strSQL As String
   
    strUrlFolder = "http://server1/exchange/grandmas.org.uk/public folders/all public folders/group contacts/"
    'strUrlFolder = "file://./backofficestorage/grandmas.org.uk/public folders/all public folders/group contacts/"
MsgBox strUrlFolder

    Set cnn = New Connection
    With cnn
        .Provider = "msdaipp.dso"
        .Open strUrlFolder
    End With
   
    If Err.Number = 0 Then
        MsgBox "Folder opened okay"
    Else
        MsgBox "Folder could not be opened"
        Err.Clear
    End If
   
    strSQL = "SELECT " & QUOTE("urn:schemas:contacts:givenName") & ", " & _
        QUOTE("urn:schemas:contacts:sn")
    strSQL = strSQL & " FROM SCOPE ('SHALLOW traversal of " & QUOTE(strUrlFolder) & "')"
MsgBox strSQL

    Set rst = New Recordset
    With rst
        .ActiveConnection = cnn
        .Open
    End With
MsgBox rst(1)
   
    rst.Close
    cnn.Close
   
    Set rst = Nothing
    Set cnn = Nothing
End Sub