Here is what i did to resolve this problem:
In order to add videos to your Favorites, you'll need to make sure that you have your YouTube channel set up. Once you do this, you should be able to add videos. There are several ways to do this:
Creating a channel name on YouTube.com:
1. In your desktop, go to www.youtube.com.
2. Click on your username and click on My Channel.
3. You’ll now be prompted to create your own channel.
Creating a channel name on m.youtube.com:
1. On your iPhone, go to m.youtube.com in your iPhone’s browser.
2. Press Sign in located at the bottom of the home page and sign in with your YouTube account information.
3. Press Menu.
4. To create your channel name, touch any of the following: Favorites, Playlists, My Videos, Inbox.
I found these steps at : https://productforums.google.com/forum/#!category-topic/youtube/mobile-and-devic es/D2okq9WHtoU