Reading Package Lists... Error!

[Aaron Solochek <aarons@aberrant.org>]

I was running an update on my sid system, and everything seemed to be 
going fine until it died with the following:

Reading Package Lists... Error!
E: Read error - read (5 Input/output error)
E: The package lists or status file could not be parsed or opened.

Everything I try to do results in this error.  When this happened, I 
noticed that /var was at 99% usage, so I deleted the .deb's in 
/var/cache/apt/archive to free up some room (there were lots of old 
.deb's there in addition to the fresh ones it just got).  I figured that 
 if the .deb's it wanted wern't there, it would just reget them. 
Anyway, I don't think that's the problem, but I don't know what file 
it's trying to read when it complains about the "Package Lists."  My 
untrained eye doesn't seem anything missing (as compared to a working 
system) in the /var/lib/apt or /var/lib/dpkg dirs.

Does anyone have any ideas as to what went wrong, and/or how to fix it?

Thanks.

-Aaron