I have LR6, Version 6.6.1 on my MacBook Pro OS X Yosemite, version 10.10.5. The software suddenly stopped loading my photos. The progress bar goes about 1/3 of the way, then stops. The program says it's importing files, but it won't progress any further. LR does find the photos on my camera (Canon 80D), but when I click the Import button, the files won't load and I have to force quit LR in order to close it. When I try to upload the files a second time, I get the message "The following files could not be imported because they could not be read". I shoot in RAW format. Prior to this problem suddenly occurring, I had no problems loading photos. Hoping there's a solution to this issue.
It seems like you have two different problems
Let's see if fixing #2 also fixes #1. This error message indicates that you do not have WRITE permission to the Destination folder. So determine what the Destination folder is (it's on the right side of the Import dialog box) and either change it to somewhere else that does have WRITE permission, or change the permissions on the exact Destination folder to WRITE permission.
Well, you were very close and most likely right. I had, for some reason, accidentally moved my destination folder. A friend in my photography club, who is pretty much a Lightroom expert, found the problem and resolved it. Thank you so much!