I've been using LR6 (on Mac) for a few weeks since upgrading from LR4. Everything has been OK until now that I can no longer import any images. When I select a device or a directory I see the "Loading dates" message in the bottom left but no thumbnails appear to select for import. The same thing happens if it is on my desktop or from a card and also if they are jpg or raw files. I have rebooted and upgraded to LR6.1 and still have the problem.