Disk Defragmenter doesn't appear to have space for degfragmentation

I have an exchange server.  It's system drive has 29% free space and is badly fragmented.  The disk defragmentation utility sees the 29% free space but states that 0% is available for defragmentation.  Why is this and, much more importantly, what can I do to defrag this disk?

Thanks in advance for any advice.
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rindiConnect With a Mentor Commented:
The windows defragmenter needs 30 or more % free space. The files shouldn't be too large either. You would get some improvement by using a third party defragger.

Lee W, MVPTechnology and Business Process AdvisorCommented:
move things off the system drive.  What's on it?  What files are "badly fragmented".  If they are that bad, you can manually defrag them by moving them to another disk, then moving them back.

Move the page file.  Move the information store.  etc.
jrubinsteinAuthor Commented:
Thanks for the reply but I have tried the obvious.  There is no page file on this drive.  The information store has been moved off it.  The drive does have, as I stated 29% free space and the disk defragmenter recognises this.  When I try to launch it the message states that there is 29% free space but that 0% is available to the defragmenter.  When I tried moving the last expendable file off the drive, I still got exactly the same message.  The drive is only 6GB in size and without reinstalling exchange I can't see how to save more space on it.
jrubinsteinAuthor Commented:
I'm accepting this answer because I have found a third party defragger which is doing the job as we speak.  However, the windows defragger will work with as little as 15% free space although an extra 12% may need to be allowed for MFT.  In this case my hard disk was so fragmented that I suspect that the free space was too finely distributed.  For the record I'm using PerfectDisk.

Thanks to both rindi and Leew for their replies
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