YouTube is unavailable (Abonnements)

Dear Apple Community!

Since 2-3 days the YouTube app give me the message "YouTube is unavailable" when I go to my abonnements and select on of them.

The "New Videos" section and the other things are working without a problem.

I tried the following:

• totally close the YouTube app & reopen it
• restart the iPhone 4S (iOS 5.0.1)
• finish and restart the abonnement via the YouTube Webpage

Anyone having the same issue? Are there any solutions for this problem, instead of restoring the iPhone... (It will make me very angry to restore my iPhone for such a crap!)

In advance I thank you for your help.

Yours sincerely,

Marc