Basically, the system would stall for a bit on shutdown, giving a CIFS error.
The error line indicates that CIFS VFS is not responding for CMD 50...
Turns out the problem was that the network manager would shutdown before my mounted samba shares could dismount.
I found this blog that had the fix:
sudo ln -s /etc/init.d/umountnfs.sh /etc/rc0.d/K15umountnfs.sh
sudo ln -s /etc/init.d/umountnfs.sh /etc/rc6.d/K15umountnfs.sh
Entering these lines will cause your system to change the order of events during shutdown, and samba shares will be dismounted before network manager goes off-line, resolving the issue.