This error indicates that BB agent is having difficulties to resolve 'Prenom Nom' in the GAL of BlackBerryServer mail profile. To check if user in question is present in the GAL please use Outlook to open up 'BlackBerryServer' profile.
In case if user cannot be found in the GAL please try to use 'Force GAL Sync' button on zcb logging control(type zcologctl.exe in command propt) to initiate GAL resync. Please note that in case of big GAL it may take some time for GAL sync process to complete.
The following article may also be helpful:
BES set to use the local contacts list instead of the GAL - Zimbra :: Wiki