FCPX 10.3.4 The operation couldn't be completed. Invalid argument

Getting the error message from FCPX 10.3.4: "The operation couldn't be completed. Invalid argument" when trying to move a clip between Events.

Well the culprit in this case is a filename containing a dot (in addition to the dot extension), something like: "clip.ver.mp4"

FCPX doesn't like the dot in the filename, so I renamed the clip: "clip_ver.mp4", relinked the file and all is good.