Volume %1!s! has %2!d!% free space, but only %3!d!% is available for use by Disk Defragmenter (due to reserved system space). ...

Volume %1!s! has %2!d!%% free space, but only %3!d!%% is available for use by Disk Defragmenter (due to reserved system space).  To run effectively, Disk Defragmenter requires at least %4!d!%% usable free space.  There is not enough disk space to properly complete the operation.  Delete some unneeded files on your hard disk, and then try again.