Following my post explaining how to synchronize a SharePoint 2013 with SharePoint Workspace (http://blog.hametbenoit.info/Lists/Posts/Post.aspx?ID=440), you may experiment issue during the synchronization with error “The field “AppAuthor” contains a lookup to list “AppPrincipals” that cannot be resolved. The target list may not be part of this site”

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This is (unfortunately) a known issue.

To solve it, just install the August 2012 Cumulative Update for SharePoint Workspace available at http://support.microsoft.com/kb/2687364