GREGWELCH (from the developer)
This sounds like it could be a known issue, which is addressed on the plugin page. Please make sure the "Number of Recent Items" setting for Documents in the Appearance panel of the OS X System Preferences is NOT set to "None." It should be set to 5, 10, 15, 20, 30, or 50. Otherwise normal copys and moves will not function properly. (Setting it to "None" does not make sense if you are going to use the plugin, but it should not break moves/copies. This will be fixed in the next release.)
I hope this fixes your problem. If not, and you still want to use the plugin, please contact me directly (welch@cs.unc.edu) so I can look into it with you.
(Version 1.0)