Try disabling the OSX Photos app. You need to do it for each separate camera, card reader or device. See this link for more information.
Otherwise ensure the Destination panel to the right of the import dialog is open and the destination folder is highlighted with the file path shown at the top. Check that the destination folder also has read & write permissions.
It should be possible to expand the panel on the left by clicking Users and expanding down the folder tree.
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Try resetting your preferences first. Instructions here:How do I reset Lightroom's Preferences? - The Lightroom Queen . Yeah u might need to deselect your catalog afterwards. If this doesn't help unplug all your external drives and other usb or thunderbolt accessories. Check if it still locks up. If it doesn't replug all your drives one-by-one.
If if none of these help, you ran into a bug in 2015.6 that pops up on some people's machines. Only fix is to revert to 2015.5. Follow these instructions: How do I roll back to Lightroom 2015.1.1 or Lightroom 6.1.1? | The Lightroom Queen but instead of rolling back to 1.1 download the updated to 2015.5 and install that. Many people have this problem. Hopefully Adobe will fix it soon.
Thanks. I ended up rolling back to 1.1 per your suggestion