Trascrivo la procedura del link di pcalmeglio:
Go into Registry Editor (Start, Run, "regedit"). Go to HKEY_LOCAL_MACHINE, S
oftware, Microsoft, Office, 11.0, Delivery. There should be only 1 directory
under Delivery, which is your DownloadCode (mine was 90000409-6000-11D3-8CF
E-0150048383C9). Select that directory. On the right side of the screen, rig
ht-click on CDCache. Change the value to 0.