Encrypted/Journaled Seagate won't accept Password
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:


Launch Disk Utility and Select the Drive that won't unlock.
Click on Verify Disk (after it finished it told me the disk needed repair), and after it finishes with the verification, click Repair Disk.
I let the computer do it's job, and after a while (about 30 min), it told me the disk couldn't be repaired, but the disk was now mounted, and working normally. Like shown in the following screenshot:




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.