youtube app not working on Samsung TV

i am not able to register youtube app on samsung internet TV model LN46C650. error "authentication failed due to network failure. try again later". already talked to samsung support 4-5 times and internet provider support, but no help. tried all possible ways to make it work - reset modem, applied latest firmware, reinstall app.now i do not have any issues registering picassa and other apps.appreciate any help...now this is the only hope...

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