OK. Well there is an error there and I am not sure why. ( Other than my error obviously :-) )

We need to look at includes/modules/pages/specials/main_template_vars.php

About line 52 you should find this:

Code:
	$sale_categories_all = substr($sale_categories_all, 1); // remove preceeding comma
First of all just comment out that line and see what you get.

I am guessing that this is a live site so I can't ask you to print stuff to the screen?