I've had the same problem with defraggler recently! I use a WinXP PC with SP2. I also have ccleaner, pagedfrg (suplied by Microsoft!) installed on the PC.
However, I've noticed recently (last month or so) that the problem noted in this thread has been occurring more and more with the same avg log files noted! i believe these file are now locked by avg whenever a program like ccleaner is run. I used to run ccleaner before defraggler and did not encounter this problem in the past! Maybe, avg have done some modifications/software updates to their log files to prevent what it might see as unwarranted access to its files so that they are locked after ccleaner is run.
Anyway, for the last few days i have run defraggler before ccleaner and have obtained 100% defragmentation! I notice that if i run ccleaner then defraggler completes with the aforementioned avg log files fragmented. To resolve this i've had to restart my pc and after boot up i've had to run defraggler first which completed 100%.
I hope this info helps all concerned!