[Process aborted due to not enough free space]

Following on from the above post:

After defragging free space and running Check Disk at startup, I decided to give it another go.

It's been defragging for about 15 hours and is now 88% complete with no errors yet, so I'm keeping my fingers crossed!

[Process aborted due to not enough free space]

I installed the latest version of Defraggler yesterday (Version 1.07.124) and left the PC defragging overnight.

Checked it this morning and found the following error message:

Process aborted due to not enough free space (or something similar)

 

The 500GB drive (2 x 500GB mirrored) has 432.6GB used and 33.2GB of free space (7%).

 

Can someone please explain why 33.2GB of free space is not enough?

 

(I didn't get this problem with Version 1.05)