Error 438 when using GetConversation on a mail item - vba

Question

I'm trying to export all e-mails in a shared inbox to excel. I'm specifically interested in how many conversations I've had, rather than all e-mails I've received.
I'm getting the 438 error on the Set conv = Item.GetConversation() line:
Object doesn't support this property or method.
This implies that Item doesn't support GetConversation, even though it is a function for a MailItem.
Public Sub ExportToExcel()
Dim objOL As Outlook.Application
Dim objNS As Outlook.NameSpace
Dim SubFolder As Object
Dim MailFolder As Object
Dim SharedInbox As Outlook.MAPIFolder
Dim objRecip As Outlook.Recipient
Dim Item As Object
Dim conv As Object
Dim store As Outlook.Store
Dim xlApp As New Excel.Application
Dim xlWB As Excel.Workbook
Dim i As Long
Dim ArrHeader As Variant
On Error GoTo MsgErr
Set objOL = Application
Set objNS = objOL.GetNamespace("MAPI")
Set objRecip = objNS.CreateRecipient("sharedmailbox#outlook.com")
Set SharedInbox = objNS.GetSharedDefaultFolder(objRecip, olFolderInbox)
Set MailFolder = SharedInbox.Folders("Archive").Folders("Sub")
ArrHeader = Array("Category", "Date Sent", "Subject", "Mails in conversation")
Set xlApp = CreateObject("Excel.Application")
xlApp.Visible = True
Set xlWB = xlApp.Workbooks.Add
xlWB.Worksheets(1).Range("A1").resize(1, UBound(ArrHeader) + 1).Value = ArrHeader
For Each SubFolder In MailFolder.Folders
For Each Item In SubFolder.Items
If (Item.Class = olMail) Then
store = SubFolder.store
If (store.IsConversationEnabled) Then
Set conv = Item.GetConversation()
If (conv <> Null) Then
xlWB.Worksheets(1).Cells(i + 1, "A").Value = SubFolder.Name
xlWB.Worksheets(1).Cells(i + 1, "B").Value = Item.ReceivedTime
xlWB.Worksheets(1).Cells(i + 1, "C").Value = Item.Subject
xlWB.Worksheets(1).Cells(i + 1, "D").Value = conv.GetTable().getrows()
End If
End If
End If
Next Item
Next SubFolder
xlWB.Worksheets(1).Cells.EntireColumn.Autofit
MsgErr_Exit:
Set emailSourceFolder = Nothing
Set emailDestFolder = Nothing
Set objNS = Nothing
Set objOL = Nothing
Set SubFolder = Nothing
Set MailFolder = Nothing
Set SharedInbox = Nothing
Set objRecip = Nothing
Set Item = Nothing
Set conv = Nothing
Set Store = Nothing
Set xlWB = Nothing
Set xlApp = Nothing
Set i = Nothing
Set ArrHeader = Nothing
Exit Sub
'// Error information
MsgErr:
MsgBox "An unexpected Error has occurred." _
& vbCrLf & "Error Number: " & Err.Number _
& vbCrLf & "Error Description: " & Err.Description _
, vbCritical, "Error!"
Resume MsgErr_Exit
End Sub