Can't restore Time Machine backup - error unlocking disk

Just got my MacBook Pro and upgraded to 10.10.2, and went to restore my Time Machine backup (on a Seagate FW 800 drive).

I went into Migration Assistant and my Time Machine backup, which is encrypted, appeared as normal. I clicked on it and went to enter my password. After I hit return, it just froze for a while. Then the dialog disappeared and it went back to the previous screen. Clicking Next would flash the dialog for a fraction of a second and then it would immediately disappear. I couldn't unlock the drive and restore my backup.

So I tried booting into the Recovery drive and I got...the same results. Still couldn't restore the drive.

I created the backup on 10.10 beta 2 and it had a slight error during the encryption declaring it couldn't be encrypted, but it got encrypted anyway (?). I can't even mount it in the Finder.

TL;DR Time Machine full backup won't restore and glitches out when trying to. Seems to be an encryption issue.