It happens to me a lot. Just sign out then in again. I think I read one of the developers say its xbox live, not the game itself causing this.
they also said it should be fixed in the last patch, but it wasnt.
no big deal tho.
Actually no, there was no such fix in the last patch as the cause of this is a mystery for us.
happens every time i start up trials as quick as humanly possible (ie. not looking at my messages or who's playing what, just immidiatly boot up trials).