A bit of googling suggests that there have been incompatibility issues with BBC iPlayer and Sony devices in the past. It's possible that the BBC has made changes to their iPlayer service that your TV set can't cope with.
Start by checking that your TV set is listed here:
http://iplayerhelp.external.bbc.co.uk/help/information/sony
If it's not, the BBC's response is likely to be that it's not their fault if you're trying to use a non-certified device. If your TV is listed there, try asking the BBC if they're aware of the problem:
https://iplayerhelp.external.bbc.co.uk/templates/bbciplayer/emailForms/emailPage
However it's worth noting that many people who've experienced similar problems in the past have reported that iPlayer has started working on their Sony TVs within a day or two anyway.