This error message
An Error Has Occurred!
Session verification failed. Please try logging out and back in again, and then try again.
came up when I clicked the "Mark as read" button. Not unusual in itself, except that I closed the tab and tried to log out from the index page. Got the same error message instead of logging out. If this happens to you with tabbbed browsing, open a different window in a new tab and log out from the new tab. Close the tab and log back in from the index page.
Quirks mode? Yep, its quirky!