LUKS in Ubuntu and changing keys

[Adam Hawes]

Hi,

I want to add a new passphrase to my LUKS partition (the root partition) in 
ubuntu but I can't seem to make it work.

I've run as root:

# cryptsetup -y luksAddKey /dev/sda5

I get

Enter any LUKS passphrase:
key slot 0 unlocked.
Enter new passphrase for key slot:
Verify passphrase:
Failed to setup dm-crypt key mapping.
Check kernel for support for the aes-cbc-essiv:sha256 cipher spec and verify 
that /dev/sda5 contains at least 514 sectors.
Failed to write to key storage.
Command failed.

Strange, because the disk is encrypted, mounts and works just fine with the 
existing passphrase.

Google does not help.  It suggested that I have a broken AES module, missing 
device nodes and a few other things that all are not the case.

What be the problem?

Regards,
A