Youtube toolbox mass unsubscribe youtube

Hello everyone, I would like to know how to remove all subscriptions from youtube.
I tried to use youtube toolbox, but when I click on the "unsubscribe from channels", I select all the channels and click on "Unsubscribe" he says FAILURE (Channel not available).
Please help me!

i did it in bulk before few days from this url: http://www.youtube.com/subscription_manager