error message after apt-get update

[Charles Kroeger <ckrogrr@frankensteinface.com>]

I was hoping someone might know what this message means after running apt-get
update:

Reading package lists... Done                      
W: Problem unlinking the file q - Clean (21: Is a directory)

I cannot find any directory named 21 or Clean. A search with dpkg -l | grep q 
Clean or 21 turns up a lot of stuff but nothing specific.

-- 
CK