make sure java is enabled , other then that sounds like you have a bad download, delete and redownload it, make sure not to click the make acceptions box before the download
uhm i really just got the blackberry so how do i enable the java and what make acception box are u talking about
dont worrie about enabling java, just delete youtube , by going to options> advanced options > application > touch youtube> menu > delete , the phone might restart thats fine , when it boots back up re download youtube, and when it gets to the blackberry download screen and before you hit download there is a little box on top of the download button it will say allow something i dont remember but DO NOT CHECK THAT BOX then it should be fine.