I am happy to see that I am not the only person with this problem but frustrated that there doesn't seem to be a fix.
Basically I have the same problem as Exarkun. When I have one product in a category, it displays as intended. If I have more than one product, no products are listed and it appears that the rest of the page is displaying fine (the footer etc). I am not sure what error display people are referring to (zen cart or php)? Not very familiar with php so not sure how to turn that on.
In addition, the category shows beside the link that it has 6 items in it. Also when I click on All Products, everything shows up fine. It is just when I click on the category that it won't show.
I tried a couple of things as well. I moved the products around to see if putting them in different categories would make a difference (in case I had set some setting up incorrect) but this made no difference. If it was the only product in the category it would show and if multiple products were attached to a category, nothing would show.
As far as I know I am not using that Image resizer. Is this something I manually have to turn on or install? I did a search in the web folder for the image resizer php file but it didn't find it so I am thinking it is a custom installed module or something?
Oh and one last thing, I've switched between templates and all of them work the same (or rather they all display the same problem). So it can't be a template corruption/editing problem and I can't see it being a database problem as the products show fine when I click "ALL Products"
Any advice would be greatly appreciated!