There are some specific items Granular Restore Option (GRO) is not able to retrieve from your Exchange data stores at this time; what specific objects were you attempting to retrieve? A limited list of what type of items GRO is unable to retrieve can be found here: http://support.veritas.com/docs/293126
On the system running the GRO, does the edbrestore.exe_run.log reporting any errors messages? Within the Exchange recovery point image, there is a sub-folder that is created called Backup Information, within it there is a file called Exchangebackup.EIF. Is the specific datastore in question listed in the file; do you notice anything unusual with this datastore with the one you are able to successfully open and retrieve from? Within the Windows event logs are there any errors for the V2I mount driver or MAPI calls from Outlook 2003 or 2007 when attempting to retrieve the public items?
Granular Restore Option (GRO) uses MAPI calls from outlook to parse the information stores stored in the mounted form of the recovery point image files. If the system running the GRO console does not have that specific MAPI *.DLL file, i suggest to uninstall GRO, repair Outlook, and install GRO again.