I've ran into the same problem with defraggler 2.5/2.1, which I had ages ago with the version 1.20 (see "Defragmenting (0%)" forever).
The problem details:
1) The drive has ~25% of free space.
2) Windows XP SP3 32-bit.
3) Lenovo B550 with 320 GB drive.
The defragmentation was running just fine up to 60%, where it stuck for a long time and didn't moving forward...
The process loads both CPU cores up to ~50%.
Restarting defraggler, rebooting the system don't help - the process sticks at the same location.
The log file (generated with /debug key) is attached.