When I tested ScanDefrag a few weeks ago I just replaced the older JkDefragCmd.exe with the latest one and it seemed to be working fine. Before you do this, rename that older version to something like "JkDefragCmd_old.exe":http://img442.imageshack.us/img442/9464/03292008062313cs3.png
ScanDefrag runs JkDefrag quite late during Windows bootup process, that's why I don't use it any more. My preferred procedure is as follows:
1) Start PageDefrag and set it to "Defrag at next boot".
2) Run disk cleanup utilities, like MS Disk Cleanup, CCleaner, etc.
3) Run registry cleaners, like Registry Mechanic.
4) Restart Windows, wait for PageDefrag to finish and exit from Windows.
5) Run JkDefrag from BartPE, VistaPE or similar environment on USB flash drive or CD.