this usually works for me when im at work. I close the youTuube app on background turn OFF the wifi on settings, then turn off my phone completely. when i turn it back on just turn the WiFi back on and go to you tube and try it it usually helps me. hopefully it helps you..
is it a jailbroken iPhone and which iPhone ? mine is a 3g and after jailbreaking I was using cydia for this problem in particular and there is a repo which I can't remember but google for "pushfix "and you should get sum pic about what to do.