SQL/DB Error message

Today while hacking away at my site, I got the following message whenever I clicked on a post:

SQL/DB 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_description FROM wp_categories WHERE cat_ID =

As far as I know, I haven’t made any changes to the SQL queries. I sometimes force the category, but this happens when I select a post from any category. Most of the changes I have been making are display-related.
I use the following new global variables:

• $sorting_function
• $sorting_function
• $posts_sort_order
• $show_info_bar
• $show_post_excerpt
• $show_cat_heading
• $show_cat_description
• $current_array
• $config_array
• $ini_file

Am I walking on anything with any of these?
You can see the problem by going to my site and clicking on any post.