unable to parse package file; aptitude effectively dead.

[hendrik@topoi.pooq.com]

While I'm waiting for someone to *fix* bug 405506, does anyone have an 
idea how to recover from it?  Is a reinstall in order?

Yesterday aptitude reported
  Unable to parse package file /var/lib/aptitude/pkgstates
This happened on an etch that was just installed the same day from a 
previous-day netinstall daily build.

The file does exist, and appears to be binary gibberish.
There's also a pkgstates.old file, about one minute older, in the same 
directory.  Should I try replacing pkgstates by pkgstates.old in the 
hope that will help?  I'm reluctant to do this without some idea just 
what role this file plays in aptitude.  It doesn't seem to be the 
downloaded, consolidated list of available packages, since updating has 
no effect on it.

-- hendrik