Upgrading Drupal

Since upgrading my site from 5.3 to 5.5 (I skipped 5.4, 5.5 was out before I knew about 5.4) I am getting the following error in my watchdog when I edit a node to update it:

[code]
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ') AND th.tid IS NULL' at line 1 query: SELECT DISTINCT td.tid FROM term_data td LEFT JOIN term_hierarchy th on td.tid = th.parent WHERE td.vid IN (6) AND td.tid IN () AND th.tid IS NULL in /var/www/tjharman.com/includes/database.mysql.inc on line 172.[/code]

I just tried to go from Zen 5.x-0.7 to 5.x-0.8 (on Drupal 5.3). The new Zen version didn't work at all. It even rendered the system inaccessible, because almost all of the stuff that should be on screen was outside of the screen on the left side. Had to use tricks and URLs to get the system back into a working state.

What could be wrong here? I used the current Internet Explorer 7.

I have a Drupal 5.3 based website.
Should I upgrade to 5.4 and then 5.5? or directly to 5.5?

It seems there have been some changes to the way taxonomy works, but I can't find any documentation of it. Does anyone know where we can find details?

Hi
I have a vocablulary, with a single term.
It is set to "herarchy : single" and "required" is checked.

So when user submitted content before 5.4, the single term was selected by default, user didn't had to change it.

Now the behavior is different, the taxonomy selection shows "please choose".

I find this to be less intelligent behavior, since there is only one term that I want selected by default and nothing to chose from.

I am in the middle of trying to convert my site from 4.7 to 5.5. I have 1 main site, and 2 sub sites. All worked well with 4.7.

When I did the upgrade, my main site went well.
However any sites I had set up as multi sites error on running upgrade.php. The error I am getting is

Fatal error: Call to undefined function user_access() in /home/ycim/public_html/includes/menu.inc on line 1376