I'm running PhotoMechanic4.6.1b0420 on the same mac system mentioned earlier on this thread.
I don't get an error message this time, but when I do command Y with delete originals selcted, the originals are moved to the new folder but appear to remain in the folder I am working from. Have done this three times now with the last time keeping the thumbnail but giving me a "unable to render image" when I try to look at it in preview mode.