I have a client with a SBS 2003 server. Recently, I discovered that the 20 GB C drive partition was almost full (less than 100 MB). Using TreeSize Free I could not find the reported data. I started moving installed programs to the data drive. After uninstalling Office 2007, I rebooted and in addition to the .5 GB program folder, approx 3.5 GB of additional space appeared after reboot. The total was then almost 6 GB, matching TreeSize. A few days later I checked and the free space had dropped to just over 3 GB. Again, I could not account for the space using TreeSize. I installed diruse and it matches the amount reported by TreeSize. Currently, they report 4.7 GB of free space, but Windows reports 3.8. Recently, I reran Set Up Monitoring & Alerts because of application errors similar to this EE question: http://www.experts-exchange.com/OS/Microsoft_Operating_Systems/Server/SBS_Small_Business_Server/Q_26200251.html?sfQueryTermInfo=1+10+30+applic+fault+wmiprvse.ex
Any ideas what might cause the miscalculation of free space by Windows? Should I trust the diruse amount instead of Windows?