To stream Hulu Live TV on your Chromecast, connect your mobile device to the same Wi-Fi network as your Chromecast, open the Hulu app, tap the Cast icon, and then select your Chromecast device. Then, ...

Disable all your Chrome extensions. If the error disappears after doing this, re-enable the extensions one by one, testing after each to ensure you don't see the Chromecast 'source not supported' ...