@Amiduffer
Sounds like something may actually be trying write something to the disk while the defrag is running, some sort of malware perhaps?
@A4000_Mad
Firstly, don't use anything Symantec/Norton. Besides which, I've done plenty of defrags with Symantec AV running no problems, must be something your doing thats upsetting it. BTW, all journaled file systems require a check of some kind if power is cut suddenly, it's all part of trying to protect your data. Ever shut an Amiga off during a disk write?