Problem moving Events into new Library

Upgraded to 10.1 a few days ago and I am tidying up some of my existing events and consolidating them into more organized libraries. On moving one event from my main drive to an external drive I get the message "The operation couldn't be completed. File exists"

I have no idea what this refers to and why this event can't be moved. Nothing special in this just a couple of pieces of raw video and two compound clips. Anyone help?

Additional. Also I have started seeing this when moving Events: I just get the spinning beach ball and nothing happens. When I look in the Activity Monitor FCP shows as "not responding" and the only way I get back is to force quit. This seems to be a random occurrence and sometimes happens, sometimes doesn't.