In Magento 1.7 for one sub-category page I get Allowed memory size exhausted errors in Gd2.php on line 51 which is:
$this->_imageHandler = call_user_func($this->_getCallback('create'), $this->_fileName);
so you'd think that some image is too big or something but when I view the category page for one level up and set it view all products on one page it displays fine. So it's showing all of the products in the problem category plus more without running out of memory.
I've checked the category configuration page and it's set the same as all of the other sub-categories and the category isn't assigned a picture and doesn't have any different layout or skin.
--More info
I created another category, named it similar, added all the same products and then both worked. If I delete either one, remove all of the products from one or the other, or set one or the other to disabled or hidden then it errors again. The error is the same but the tried to allocate amount changes from 13824 to 3456 bytes (out of 128mb).