There can be two reasons for this :
1. SE C902 is a java phone and it does not support Adobe Flash, so, the website www.youtube.com will not work for viewing videos. If you visit the website, that is exactly what you will encounter.
2. The wapsite m.youtube.com or wap.youtube.com should work fine on your phone provided that you have the correct streaming configuration settings. This site does not use Flash, but it streams the videos as 3GP over your 3G or EDGE connection. If you do not have 3G or EDGE, streaming content does not work over GPRS connection.
I suggest that - check your internet settings and see whether you have correct streaming configuration settings and a capable connection.