1) You need to change the MessageClass on the existing items to point to your new form's class. See http://www.outlookcode.com/d/newdefaultform.htm#convert for several tools and scripts to accomplish this.
2) Could be that some users are using a cached Public Folder\Favorites folder, so more than one person is updating the contact, then syncing their changes.

Signature
Sue Mosher, Outlook MVP
Author of Configuring Microsoft Outlook 2003
http://www.turtleflock.com/olconfig/index.htm
and Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers
http://www.outlookcode.com/jumpstart.aspx
> Hi,
>
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>
> Thanks for your help