I upgraded to Symbian Belle. I am able to search and browse videos but not able to play videos.
This is not the problem with FastTube. Problem is with the settings of default Symbian Video Player. Please check the Video Player settings at Settings->Application Settings->Videos->Access point is use. Here set the access point you want to use to play videos.

Sometimes I do not see any option to play HD videos.
All videos on YouTube are not in HD. You will see option for HD video if it is available.