Sometime you receive “Unable to display this Web Part. To troubleshoot the problem, open this Web page in a Windows SharePoint Services-compatible HTML editor such as Microsoft Office SharePoint Designer. If the problem persists, contact your Web server administrator.”
After you’ve backup/restored site using sharepoint designer 2007 in a page where you have customized a data view webpart [new, edit, view page of list].
The most likely reason for this error is that the backup/restore operation basically changes the list id in the new server, so in your customized data view page where this error is happening, open the page in SharePoint designer and replace the old list id with a new list id, and voila! It will work!
Hope this helps!
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