I just updated my NV+ from 4.1.6 to 4.1.8 so that I could use it with Lion in an iMac and AFP. The update went smoothly, but as soon as I tried to access it I got the message about CNID DB, which I have never seen before. It says switching to read-only mode. It does not seem to be fully consistent. I got the message first with the Lion machine, then did a file system check/reboot and went to an old Leopard machine and got the message. Immediately after that I did not get the message on the Lion machine and was able to access, then the message came back.
The Log only shows that no errors were found in the volume check. Incidentally - the logs seem to have switched to Swedish. I have switched them back.