Affected versions: 2.1.x, more?
First seen: December 2007
Have the host delete the relevant txt file in /tmp
Check the uploads path (settings / miscellaneous)
Upgrade Restore Backup Database
If you have no backup, you can try the following SQL to help return posts to pages.
UPDATE wp_posts SET post_type = 'page' WHERE post_parent !=0
UPDATE wp_posts SET post_type = 'page' WHERE menu_order<>'0'
Remove damaged files. (More detail needed)