Vista - Vista Ultimate

Since installing RTM a number of web sites I used to be able to listen to
(or watch on some) no longer will play. They worked in RC1 just fine. I
tried with the basic installed package and with the codec package I used in
RC1. In both cases, the site launches a panel that just appears faintly for
a few seconds then disappears. In RC1, this would be followed by the
launching of Windows media player. In other cases the ads will play but
when it switches to the main broadcast the player will buffer then just
stop. Anyone experienced the same or similar problems and solved them. Was
WMP11 changed between RC1 and RTM? Any suggestion welcomed.