[Outlook] Runtime Error...Outlook 2007 bulk-convert Email1Address, VERY strange

I want to change the e-mail address of all contacts in Outlook to lowercase and remove whitespaces.

Code:

---

Sub ReFileContacts()
 Dim items As items, item As ContactItem, folder As folder
 Dim contactItems As Outlook.items
 Dim itemContact As Outlook.ContactItem

 Set folder = Session.GetDefaultFolder(olFolderContacts)
 Set items = folder.items
 Count = items.Count
 If Count = 0 Then
 MsgBox "Nothing to do!"
 Exit Sub
 End If

 'Filter on the message class to obtain only contact items in the folder
 Set contactItems = items.Restrict("[MessageClass]='IPM.Contact.112607'")

 For Each itemContact In contactItems 'Loop through all contacts
    itemContact.Email1Address = LCase(Trim(Replace(itemContact.Email1Address)))
    itemContact.Save 'Save the contact
 Next

 MsgBox "Your contacts have been converted to lowercase without whitespaces."
End Sub

---

These contacts use a custom form hence the IPM.Contact.112607

When I run this (Contact folder has 20.000 contacts) I get the following error:

runtime error -1836974071 (92820009)
one or more items in the folder you synchronized do not match.
to resolve the conflicts, open the items and try the operation again

I really have no idea where to go from here...
I did NOT expect this kind of error.

If you run this script in your Outlook, you will definitely not get this error.
If you do, make sure you change

Set contactItems = items.Restrict("[MessageClass]='IPM.Contact.112607'")

to your corresponding form.

Please note:

I know that the field is called Email1Address because msgbox(itemContact.Email1Address) returns the E-mail address value.

Thank you!