When I move files and paste in another location, sometimes I make a mistake typing yy instead dd. Then I can't find any means to cancel the copy operation.
Try Ctrl-C. It worked for me. I got it from this discussion: https://bbs.archlinux.org/viewtopic.php?pid=1211500
Press w to display all running/queued operations, move (with j/k or arrows) to the desired operation and press dd to cancel it.