aptitude/apt: "could not lock the cache file"

["Monique Y. Mudama" <spam@bounceswoosh.org>]

Argh!  Not sure what's going on here.

I fire up aptitude, hit 'g' to look at what's about to be
installed/removed/whatever, hit 'g' again, download completes[1], and:

                Apt errors
W: Warning: could not lock the cache file.  Opening in read-only mode
                 [ Ok ]


Well, that's a bummer.  I don't have any apt or dpkg related process
running ... and besides, it doesn't actually say it couldn't get a lock
file; it says it couldn't lock the cache file, which seems like a
different statement entirely?  I did nuke the following:

rm /var/cache/apt/archives/lock
rm /var/lib/aptitude/lock
rm /var/lib/dpkg/lock
rm /var/lib/apt/lists/lock

based on this link: 

<http://www.mail-archive.com/debian-user@lists.debian.org/msg92551.html>

... no effect.

I'm guessing fuser would be helpful here, if I knew the name of the
cache file.  I tried `fuser /var/cache/apt/pkgcache.bin` and got no
output.

The bug lists for aptitude and apt don't seem to be pertinent, although
there are enough bugs listed in the apt package that I might have missed
something.

Any ideas?

[1] Download is actually empty, as I updated my package list about a
week ago.  The theory is that I can let packages sit on the server for a
few days and then see if any new bugs have been filed before I actually
update my system with these new packages.  Also, I'm sucking packages
down through apt-cacher, not that I would think it matters.

-- 
monique