If the TV cannot load YouTube successfully, here are some methods for you to do the troubleshooting:
1. Check whether YouTube is the latest version. If not, uninstall it and upgrade it to the latest version.
2. Check the Time and Date on the TV.
3. If the Time and Date are incorrect, please try to correct the Time and Date and load YouTube again.
If Time and Date are correct, please try to update the software of the TV online.
Press the Settings 
button on the TV remote, then select Settingsà System à About à System Update à Network Update:
