Have you seen anything like this before?
In my case, if I load my Kontakt 4 sampler (as standalone) with external USB hard disk with time machine backup system activated, the disk just shuts down and never comes back again. And if I plug the USB port again, I get the message ‘The disk you inserted was not readable by this computer.’ and the disk is still not operational. I can’t understand the whole situation, but I assume it’s some kind of logical error on the Mac OS file system.
Anyway, since I was using it as a backup drive, I just did a clean format and backup the system from scratch. But after some research, I’ve found out that it can be fixed very easily with a single terminal command.
If you get the message above, click ‘Initialize’, then ‘Disk Utility’ will pop up. Ignore disk utility, and run ‘Terminal’, then type
(insert your hard disk ID instead of disk3) Type in the password if asked. It’s done. try to plug in your USB port again and check if it works. Of course all of your data should be fine.