For me the problem is intermittent. For example...
1. I'll connect the Aura HD to the Mac and wait for the devices to show on the desktop.
2. Then I run Calibre.
3. Calibre tries to connect to the database, but fails.
So I unmount the devices, quit Caliber and go to step 1 again.
Sometimes I need to do this three or four times before Caliber eventually manages to connect to the database.
For me the problem is intermittent. For example...
1. I'll connect the Aura HD to the Mac and wait for the devices to show on the desktop.
2. Then I run Calibre.
3. Calibre tries to connect to the database, but fails.
So I unmount the devices, quit Caliber and go to step 1 again.
Sometimes I need to do this three or four times before Caliber eventually manages to connect to the database.