I just learned a new way of breaking your store:

1. Login as admin
2. Under Configuration -> Layout Settings change the value of the setting ‘Categories - Always Show on Main Page‘ to0 (zero)

This will break both zen-cart and ZenMagick unless a valid category is configured with the setting ‘Main Page - Opens with Category’.

interestingly enough, ZenMagick will work if the setting ‘Main Page - Opens with Category‘ is changed from the default 0 (zero) to an empty string.

zen-cart on the other hand will return something like the following in both cases:

1054 Unknown column 'CATEGORIES_ROOT' in 'where clause'
in:
[select cd.categories_name from zen_categories c, zen_categories_description cd where cd.categories_description LIKE '%-SITE_NAME-%' AND cd.language_id=1 AND c.parent_id = CATEGORIES_ROOT and c.categories_id = cd.categories_id and cd.language_id='1' and c.categories_status=1]

EDIT: I just realized that the above error is the result of a different zen-cart mod installed. It looks like it does work as expected - my mistake!