For the last week or so, it's been impossible to import anything into a Motion 4 project - either dragging or using the "import" button - without the application hanging. If you layer up all the assets in FCP and then send to Motion, that works, but if you want to add anything else once you're in Motion, you're screwed.
I trashed the prefs - didn't fix it. I removed and reinstalled Motion - didn't fix it. I removed and reinstalled the entire FCS - didn't fix it.
I'm now assuming that perhaps it's an OSX issue rather than a Motion one, especially since the only new thing that's been installed on my Mac recently is the most recent OSX security update? This is a serious PITA. I suppose it might be an incentive to upgrade to Motion 5, but still.