Clients attempting to search a public folder that is in a mixed Exchange 2003/2010 environment may encounter the following information message, and will not be able to search the public contacts, etc. ERROR:
CAUSE: Side effect of having public folders in a mixed exchange 2003/2010 environment. WORKAROUND: The only “bandaid” workaround I have found is to add the pub contacts, etc. into favorites, then put the outlook client in cached mode, enabling the cache mode option to download public folder favorites, and making that public folder a favorite. Inside email accounts, server settings enable the use cached exchange mode 
Inside “More Settings”, enable the checkbox for download public folder favorites 
Clients will be able to search the pub fixed contacts, etc. after outlook is restarted and has finished updating the local offline file.
