[support] Upgrade from 6.16 to 6.22 - should it break things badly?

[Chris G]

I just recently tried to upgrade a Drupal 6.16 installation to the
recommended 6.22.  It fell in a crumpled heap!  I did the upgrade using
drush and it produced loads of warning messages about disabled modules
because the 'module wasn't compatible with the new version' and also did
some database changes which I'm pretty certain was what broke the system
completely. 

I have reverted to 6.16 and restored the database and all is well now,
but I'm a bit unsure how to proceed as it feels as if I really should do
the security upgrades.

I'm afraid I lost the output from drush where all the warning messages
were shown because I just wanted to undo the mess.

I can possibly try again with (yet another) copy of the site and show
the error messages here if that might help.

-- 
Chris Green