I run a

sudo aptitude full-upgrade

On my Debian Lenny, but once all the packages were downloaded and started to be installed, suddenly the process stopped, then when I run

sudo aptitude reinstall

I got this:

sudo aptitude reinstall
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Reading extended state information      
Initializing package states... Done
Writing extended state information... Done
Reading task descriptions... Done         
The following partially installed packages will be configured:
  cups-driver-gutenprint cupsys-driver-gutenprint debian-faq gxine 
  libregexp-java menu 
0 packages upgraded, 0 newly installed, 0 to remove and 170 not upgraded.
Need to get 0B of archives. After unpacking 0B will be used.
Writing extended state information... Done
dpkg: error processing iptables (--configure):
 package iptables is not ready for configuration
 cannot configure (current status `triggers-awaited')
dpkg: error processing nano (--configure):
 package nano is not ready for configuration
 cannot configure (current status `triggers-awaited')
dpkg: error processing debian-faq (--configure):
 package debian-faq is not ready for configuration
 cannot configure (current status `triggers-awaited')
dpkg: error processing cups (--configure):
 package cups is not ready for configuration
 cannot configure (current status `triggers-awaited')
dpkg: error processing libxine1-bin (--configure):
 package libxine1-bin is not ready for configuration
 cannot configure (current status `triggers-awaited')
dpkg: error processing libregexp-java (--configure):
 package libregexp-java is not ready for configuration
 cannot configure (current status `triggers-awaited')
dpkg: error processing menu (--configure):
 package menu is not ready for configuration
 cannot configure (current status `triggers-awaited')
dpkg: ../../src/packages.c:221: process_queue: Assertion `dependtry <= 4' failed.
E: Sub-process /usr/bin/dpkg exited unexpectedly
A package failed to install.  Trying to recover:
dpkg: ../../src/packages.c:221: process_queue: Assertion `dependtry <= 4' failed.
Reading package lists... Done             
Building dependency tree       
Reading state information... Done
Reading extended state information      
Initializing package states... Done
Reading task descriptions... Done  

So, after googling a little, I used dpkg to uninstall manually all the packages listed above,

sudo dpkg -r cups-driver-gutenprint cupsys-driver-gutenprint debian-faq gxine

Then the command

sudo aptitude reinstall

worked again, and I was able to install those packages again.