Any time you upgrade any module, you may temporarily receive messages until you do the update.php. This is especially true if there are schema or theme changes. I don't know if there are any between 6.16 and 6.22.

All the interim releases are still available on DO, so you can always go back and do smaller changes. I always test updates on a local copy of the site to make sure that, no matter how well tested, they don't break MY site. This is why I carefuly read the security announcements and don't run the Update module on my live sites.

Nancy

Injustice anywhere is a threat to justice everywhere. -- Dr. Martin L. King, Jr.

From: 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.