I had this problem with both posts AND pages immediately after upgrading to version 2.7. This issue caused my published pages to not be recognized, thus no pages were displayed on my site because wp_list_pages() returned nothing, although the pages appeared in my admin console (under all pages, though none were displayed under published pages, even though all were in status: published). This also impacted my posts, which were in draft status - the admin consoles Edit Posts page said I had four drafts but when I clicked the Drafts link it would say "Error : Not Found Sorry, but you are looking for something that isn't here".
The solution for me was to use the command repair table wp_posts (can be executed by typing this command in the SQL Query window of PHP MyAdmin for your wordpress database).
In my case, this table had somehow become corrupted. If you are having this kind of problem with your posts or pages, you might check this table, which contains the content for all of your posts and pages (which are apparently a special kind of post).
I diagnosed this problem by running this query which returned an error that told me the table was corrupt:
SELECT * FROM
wp_posts order by