I'm running Yosemite on late 2014 MacMini, and external drive 1TB drive connected via usb. Few days ago the system started to ask me for a password for the external drive, I'm not running this vault thingy and none of my password worked. So I decided to format the drive and partition it again. Now the drive is connected without any problems, but soon after I'm starting Time Machine it disconnects and reconnects, of course, the backup fails. I'm not really sure how to approach this issue, help required. Thanks.