HotAir has the link to the signing video from the Telegraph. Apparently Mr Obama was heard to ask the dean what the day’s date was – but managed to get the year wrong.
A Westminster Abbey spokeswoman confirmed it was the president who had written the wrong date.
The White House is pleading jet lag.. http://hotair.com/archives/2011/05/24/the-obligatory-obama-thinks-its-still-2008-post
Jet lag? He was probably sleeping the entire trip.