Not really into youtube so I am not familiar with how they react with a berry but have you tried clearing the cache on the BB? Have you installed any recent apps? What is the error message?
Yup cleared the cache. No dice.
Error message is "error playing" "an error has occurred attempting to play media"
As far as new apps since yesterday.. I downloaded a free GPS program but have since deleted it because i didnt like it.
Other than that i have deleted some apps that i dont like or wont use to free up memory. None of those would have an effect on this... At least i dont think so.
It seems playing You Tube is hit or miss. Someone the other day suggested that the network was not able to keep up with the demand so it would say an error in the file. Kind of makes sense to me.
You may want to try Http://www.tinytube.net. It has most of what you would find on YouTube and you can download them to your BB if you want.