I know this thread is old, but I've just installed Joomla and K2. "Latest items from (one or more) users or categories" isn't working for me either. I'm testing this on Joomla 1.5.x and the K2 2.4.1. I made some K2 categories and K2 Items, but all I get is a blank component. (Everything else loads, template, modules, etc)