I have a network installation used for project management at mydomain.com/client/. The installation has a number of sub-blogs in folders below that (i.e. mydomain.com/client/proj1, mydomain.com/client/proj2, etc.).
After installing this plugin at the top level and clicking "network activate", pages and posts stopped showing up in the sub-blogs even though they were still correct in the database. From the front end, it simply gave me a not found message for posts and pages. At the back end, the post/page managers showed a correct number of posts at the top (i.e. All (17), Published (10), Drafts (7) ) but then says "Posts Not Found" underneath and gave me no option for managing them. This was true both for already existing posts and new posts which were created after activating the plugin.
After deactivating the plugin (I deleted its folder rather than deactivating/deleting from WordPress) the posts reappeared and everything's acting as normal.
I'm using WP 3.0.3 with a custom theme, modified from Twenty-Ten source. I deleted the plugin without remembering to look at the version number, but it was installed from the WordPress plugin directory on Dec. 28, 2010.