Error Publishing New Pages

Hi there, I installed a new image gallery plugin (FlAGallery) and since then I'm having issues publishing pages. Specifically pages posted under a parent page. I can post them fine when they aren't under a parent but when I choose for them to be under a parent I get an "error 404" message when trying to view the published page. I've tried deactivating the FlAGallery plugin and reacting the NexGen Gallery plugin (which worked fine) but that isn't solving the problem. Please help.