Tried that too! :(
I sampled a few posts around the Internet, Lion is getting some mixed reviews, so I have put off upgrading.
During one of the moves I tried within iMovie, 7 of the 8 files were copied completely. So after rebooting -- since every time this problem happens, Finder seems to hang as well -- I manually deleted the last incomplete file and tried copying only the one file, also the largest, at 16.65GB. That one file transfer hung as well.
My OS is 10.6.8, all software is up to date that I know of as of this version.
I have never had a problem with all my Firewire devices. The problem has only arisen since adding this native USB 3.0 device that has backward USB 2.0 compatibility. Is it possible that is part of the problem?
Thanks for the ideas!