I've had the same problem.. I've herd of one member having luck by using his old DroidX cable. The most popular solution is to use a file transfer app.
Android.com
You need USB Debugging turned OFF for it to work... also the program is buggy and doesn't always work so well but its the only solution I've found for connecting a GNex to a MAC.
@dmmarck..... are you able to connect and transfer files between your Mac and phone?
Yup. Do it all the time, with either an old Blackberry microUSB, my HTC DINC microUSB, or the Samsung microUSB. Tricks I've learned over the past few months:
(1) Lock screen must be off or else it goes nuts, at least 80% of the time.
(2) Debugging, like you said, must be off. At worst nothing shows up, at best half your stuff shows up.
(3) Use the furthest USB port (ie the one closer to the monitor)
(4) When you need to restart it, always unplug and replug it in. Restarting the app rarely--if ever--lets you get past the little error message that comes up.
(5) Rewriting files will cause it to lock up (the program); same with trying to move bigger files, occasionally. Also, it's a massive pain to move files WITHIN the folders, so what I do is simply copy them to the Mac, delete from where they are, and then drop them into the correct folder.
In fact, when it's plugged during flashing I get relieved when the error box pops up on my Mac b/c that means I'm out of the woods

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