Either try running Defrag in Safe Mode and/or download and run ScanDefrag
v5.0.

This is a FREE utility, written by several well respected contributors to
these News Groups and has been designed to run several original MS utilities
through a 'filter' which eliminates the usual junk which stops Defrag (and
Scandisk) from running properly in Normal Mode - as you are already
experiencing <g>

You can get ScanDefrag at either of the two sites below - and be sure to
read the associated notes for setting it up:
http://home.earthlink.net/~bblanton2/scandefrag/main.htm
http://www.blueorbsoft.com/scandefrag/index.html

HTH and good luck

Mart