When searching for a page I want to edit in admin, I get the error message:
Are you sure you want to do this?
Please try again."
By a process of elimination I have discovered that this only occurs when Regenerate Thumbnails is active.
When the plugin is deactivated, the issue disappears and even when this is the only active plugin, the issue reappears. The issue appears to be theme independent as well as the issue occurs when I activate twentyeleven with no other plugins.