I suggest a test: take a file directly off the camera and copy it to a folder on your hard drive via the Finder. Once copied, try to open it with Lr. If it fails, then PM is not likely the culprit because in this test PM was not involved. If it succeeds, then browse the folder you just copied your image into with PM. Make no changes to the image. Try and use Lr as an editor with that image. If it fails, then it may be that Lr is not responding well to the 'open' command that PM is sending it. Try drag and drop from PM to Lr instead.
Beyond that for a problem like this, I suggest contacting our support folks at:
By email: support@camerabits.com
By phone: +1 503.547.2800 option 2
Hours: Mon-Fri, 9:00am-5:00pm [PST/PDT]