Because YouTube change it's player source several days ago, the rule to download video is broken.
Now, the issue is fixed in the new version 2.3 and 2.3 is submitted to Apple for review, so please be patience, you can update as soon as Apple approve the new version
Before the new version 2.3 is approved, you can update the rule manually follow the steps below:
1. Open your Mediaburner app on your device.
2. Click the "+" button on top left corner.
3. Click the middle "HERE" link on your device
Customer support service by UserEcho