outlook 2010: autocomplete stops working
when a specific outlook client does not have persistent autocomplete functioning for Global Address List lookups try doing the following:
in the Outlook 2010 client, go to File->Options->Mail->Send Messages
then choose “Empty Auto-Complete List” and close the Outlook client
apparently, when autocomplete stops functioning it indicates something is not quite right with the stream_autocomplete file in %userprofile%\appdata\local\microsoft\outlook\roamcache. when the auto-complete list is emptied then a new stream_autocomplete file should be created.
the following article describes using a nk2edit utility (i have not tried this): http://blog.chron.com/helpline/2012/08/repairing-outlook-auto-complete/
sources:
http://social.technet.microsoft.com/Forums/en-US/exchangesvrclients/thread/69d72432-4726-4e40-a71b-048033ee33a0
http://www.itechtalk.com/thread9945.html