I have a 2011 MacBook Pro Intel running Mountain Lion. I have a 2tb Seagate External Drive with 3 partitions: all three were set up the same way with different passwords as a person who used to live here was burning DVD's from my digital backups I felt the need to do so. I was having no issues with this for the first six months I had the drive set up like this but about two months ago this changed. I can no longer mount one of the partitions. It will not accept the password I KNOW goes to it. All I can figure is that, some how, the system encryption key must have been damaged. The only other pieces of Info I can give you is this. First, I didn't use firevault for this but Disk Utl. Second, at times, I can mount one of the other drives and even though I get the "shaking window" as though I typed in the wrong pw it still mounts the drive. Odd.
Same problem here. Read and on and I'll tell you what I did to solve this problem:
I do Time Machine to an encrypted external Hard Disk. I stored the password to the disk in the default Keychain, and the system mounted the disk automatically after plugging it in. But suddenly, last morning, after I plugged in the disk, it prompted me for a password (it never did, since it was set to remember the password). In that dialogue, type a wrong password and the dialog does the wrong-password, shake animation, and it prompts for a password again; but type the correct password and the dialog freezes, like this:
The solution I have found to work is as follows:
And now, my Time Machine drive works normally again:
So, launch Disk Utility, then Verify and Repair your faulty disk as needed. This worked in my case.