Display hierarchical post types and taxonomies a single level pages at a time.
NO! This is the first rule of plugin development. Never ever change or touch core files, settings or database schema.
Not possible. Double check that you deactivated the 'pages-children' plugin. When active the plugin uses filters to alter the way the page listing is displayed. So once deactivated these filters are no longer used. See first question about changes to core WP code.
= Does the plugin work on other post types? YES. As of version 1.4 the plugin now works with any custom post type which is setup as hierarchical.
= Does the plugin work on Taxonomies? YES. This was added in version 1.5. now taxonomies defined as hierarchical will be presented similar to post types, one level at a time.
= I'm using an admin theme and the plugin stopped working I've only tested the plugin using the default WordPress admin interface. Note the plugin relies on some specific structures of the output tables used for the listing. If the admin theme you are using changes this then my plugin code will no longer work. Sorry.
= I'm using the WP-ecommerce plugin and Pages-Children stopped working. What can be done? Not much. For some reason the WP-ecommerce plugin effects the logic of the Pages-Children plugin. I've not been able to figure out the conflict. But continue to investigate.