Although your 2006 S2R is only Euro 2, it nevertheless meets the ULEZ exemption criteria (i.e. it emits less than 0.15 g/km NOx).
You need to get a copy of the Certificate of Conformity and register it with TfL.
This thread is useful and also shows other S2R owners who have already registered their bikes and may be able to give you a copy of the CoC.
http://www.ukmonster.co.uk/monster/s...ad.php?t=57125