Ignore the message from OneCare in the Tune-up Report.
What OneCare does is run a timed defrag of the drive using the same defragmenter that is already built into Windows, but it does not analyze the drive first. It runs until time is up and moves on. You are still benefiting from the Defrag process. Even when the Defrag is complete, the file system is already fragmenting again. So, the warning is really informational and can be safely ignored as there is *nothing* you can do to have OneCare complete the Defrag except perhaps to run Tune-up repeatedly all day long and never write new files to disk.
-steve