I have been unable to import files from my Canon 7D, Canon 5D Mk3, or my Sony Nex 7.
Why not? What happens? Describe in detail. Also, if there is an error message, quote it word-for-word.
Anything else I try results in a dialogue box that tells me the images can't be imported.
What's the "anything else" you tried?
When I try to import anything, a dialogue box pops up, titled "Import Results"
Below that, it says "Some import operations were not performed",
Then, below that, it says "The following files were not imported because they could not be read." And it then lists individually all the images I tried to import.
I then have the option to "Save As", or "Ok".
When I click "Ok", it ejects the card, and "No photos in Current Import" appears in the middle of the screen.
The "anything else" has been putting the CF card in the card a card reader.
Putting the SD card (sony) into the SD card reader built into the iMac.
And plugging a USB cable into the camera body.
With LR4, I just put the card in the card reader (Kingston brand), and the files import without a problem.
The “could not be read” means the DESTINATION in the upper-right of the Import panel is pointing to somewhere that the copy phase can’t copy to, so when the actual import phase happens, the files are not there to be read.
This means you don't have WRITE permission to the destination directory. Change your permissions.
For future reference, if there's an error message, you ought to state the error message in your first message.