iMovie freezes when importing video

I am using iMovie 10.0.6 and trying to import video from a JVC Everio GM-HM320BU. I have been importing video without problems for quite some time, but always from the main memory of the camcorder. Recently I had to record some video on the SD card installed in the camcorder as extra memory. I received the error message "iMovie cannot import your selection" and iMovie froze. I had to "force quit" iMovie. After reading a bit, I realized I should have imported the video on the SD card via a card reader and that it cannot be import in the usual manner.

But now I get the same message from iMovie every time I try to import video, even from the main memory of the camcorder, and iMovie freezes. It appears iMovie needs to be reset so it can import video from the main memory. HELP.