[trekchick]

I also have a MacBook Air and a PRS-350. I've not had the same trouble, but here are some questions/ideas in no particular order:
1. Try the other USB Port and/or a different cable.
2. Does the device mount properly? Can you browse its contents with Finder?
3. By default, Reader Library automatically opens when the Reader is attached. Does it?
4. Change Reader Library's Preferences to NOT open automatically, then quit (Cmd+Q) Then connect the device, make sure you can see it in Finder, then open Reader Library.
5. Quit Calibre or any other program that might try to read/write to the Reader before opening Reader Library.
6. When you say "reset" do you mean you stuck a pin in the reset button and rebooted, restored factory settings, formated internal memory, or something else?