[wp-hackers] Upgrade not completing

[Podz]

The blog has a database size of at least 60meg. No stats, no extra stuff 
- just posts and comments make that size.

Some code:
Posted by <em><strong><?php the_author() ?></strong></em> in <?php 
the_category(', ') ?>

That produces the error:
"Posted by XXX in

WordPress database error: [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 '' at line 1]
SELECT category_nicename FROM wp_categories WHERE cat_ID= "

Viewing the blog from the Manage Posts screen, that error is repeated 
once per post per category.

Underneath that error though, the category is linked as such:
http://www.example.com/blog/archives/category/
which is wrong as the name of the cat, though visible as the link, is 
not actually there.
Searching the forums finds nothing on this error.

If I try to run upgrade - because all the code is fine and 1.5.2 - it 
stops after ~34 seconds every time. It does not complete the process. Is 
this therefore a failed upgrade problem and if so, can it be overcome ?

P.