This is a general error that could appear for a number of different reasons, but is usually pretty easy to fix. Try the following troubleshooting steps:
Power off your device, then let it sit for a full 60 seconds. You can do this by holding down the power button at the top of your device, then following the on screen commands to fully shut down the device. After 60 seconds, hold the power button down again to turn the device back on.
Delete the Hulu Plus application and re-download it from the App Store. To uninstall, locate the Hulu Plus app on your home screen. Press and hold the icon until it wiggles. Then, click the "X" at the top left of the Hulu Plus icon to delete the app. Once the app is uninstalled, go to the App Store and search for Hulu Plus to reinstall.
Connect to Wi-Fi to ensure a more stable streaming experience.
If this did not help, contact us directly and let us know what troubleshooting steps you've already tried. We'll be happy to investigate further.