Thanks to ePost for suggesting the Secunia PSI program. I ran it and discovered that I had 4 different versions of the Flash plugin on my computer. I followed instructions in a Secunia forum post and uninstalled all old releases, then installed the lastest 10.x versions. Not sure if this was the issue, but I did finally deal with this important update.
I also rebooted twice, then suddenly Defraggler is working again! Could be that rebooting itself solved the problem