By chance I found that AdBlock, in firefox, was enabled.
Disabled it for BT and I can now watch BT Sort.
Hope this helps someone.
Win XP SP3 on laptop.
Will confirm PC tomorrow.
neither computer works now.
I can watch online TV without problem.
There must be an easier way.
Tried everything in the help files. None of my pc's or laptops work with BTSport.
Spent too much time trying to get this to work, will give up till BT changes the way it transmit the programs.