If you have Zen Cart 1.2.x with Ultimate SEO contribution running on MySQL 5.0.x, you will probably very soon run into the following error, preventing even your front page from opening:
1054 Unknown column 'p.products_id' in 'on clause'
This is a bug of Ultimate SEO contribution. To fix it you will need to replace two occurrences of the following two lines:
FROM ".TABLE_CATEGORIES." c, ".TABLE_CATEGORIES_DESCRIPTION." cd
in includes/classes/seo.url.php with these lines:
FROM ".TABLE_CATEGORIES_DESCRIPTION." cd, ".TABLE_CATEGORIES." c
as pointed out in this post on Zen Cart forum.