If you use social media clients then it's vital to stay up to date, since they tend to change ther APIs quite often. YouTube and Facebook implemented changes recently and if you're a Gravity fan then you'll be seeing errors unless you keep right up to date with the latest beta. In this case version 2.80 Build 7269, dated yesterday, 20 Dec 2012, available now for Symbian^3/Anna/Belle class phones here. Screenshot proof below.

From the blog post:

Smaller Installation Packages for Specific Symbian Platforms

Download for Belle, Anna, S^3 and S60v5 with Homescreen Widget Support

(DBG7269gravity.HSW.sisx, 883 kB - For Nokia N8, 808 PureView, E7, .. and Nokia N97, N97mini, C6-00)

Using Gravity as your YouTube client seems odd at first, but it works very well indeed for new items from your 'subscriptions'. It's just not a general purpose 'search and watch' client (that'll be CuteTube's territory!)

Here are some screens of the new build of Gravity in action:

When watching YouTube videos via Gravity, be patient for the buffering to complete, before the video starts to play - it's often a few seconds. And, if the video stops playing because it's run out of data (buffer), just wait a second or two and tap on the play icon again.

PS. Having mentioned CuteTube above, there's a whole new version of this due to appear in the New Year - watch this space for more.