Try to do the following:
Close the AC client software on each PC.
Open file:
C:\Program Files\Cisco\Call Manager Attendant Console\userlists\CorporateDirectory
Check if that file contains information about users. If the file does not exist, is empty or contains error messages, please delete it and then restart the TCD service in the CallManager server:
start > programs > admin tools > services > right-click on service
"cisco telephony call dispatcher" > restart this service.
Check if the CorporateDirectory file contains information now. If so, close that file. Open the AC client software on your PC and try to use the "all users" feature.