I activated disk encryption for my Ubuntu 15.10 64bit installation and get every time after entering the (correct) password the error message:
cryptsetup: unknown fstype, bad password or options?
But after few seconds (without any further interaction) this error message is replaced by the expected message:
cryptsetup: sda5_crypt set up successfully
That's it and the system is started.
Any suggestions what could be the problem? Is it merely cosmetic or serious?