Obsidian's Rob McGinnis stopped by the official Neverwinter Nights 2 forums to warn everyone not to install the latest patch via the autopatcher. Apparently it will overwrite your CD key(s):
There is currently a patch available on the Autopatcher. DO NOT INSTALL THIS PATCH!
If you do, it will overwrite your CD Key(s) and cause you much havoc.
If this patch has already been installed, you will need to manually open the file "nwncdkey.ini" and replace the CD key(s) with the original keys you entered at the time of installing the game. The file can be found in the NWN2 install folder.
If you have a backup of nwn2cdkey.ini from after you installed MotB, you can instead just restore the file from your backup.