I had the same problem on my bravia KDL- 43WD750. Nothing helped me to solve it. Many times resetting either modem or tv, factory settings etc.
If your router supports WPS then you have luck. Just turn WPS fucntion on by simply pressing the button on the router, and connect via WPS on your TV then refresh the internet content. Afterwards you can connect to wifi normally by just scanning the wireless connections. In this way the WPS fucntion will be turned off.
It worked pretty fine with me. Eventually I reset both the modem and the tv. It worked still fine.
Note: If you have to connect via WPS again then you have to touch the button and perform the further instructions as mentioned above.
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