Comment 2 for bug 53475

> Did you check if the dm module is loaded?

unfortunately not. Because I never need to manually load the module and automatic mounting of the cryptdisks partition during system boot did work correctly since I installed Kubuntu 5.10 past year.
To be honest, in the meantime I found the correct module name for the required module (dm-crypt), the error message wasn't real helpfull.

After "modprobe dm-crypt" cryptdisks will start correctly.

So the final question is, what happened that a manual module load is required and the automatic mounting during system boot doesn't work anymore after a kernel security update.