We just don't execute it well at all. The offensive line does not sell it. This is prolly why the play gets blown up more times than not. The linemen either release too quickly, don't get out to block after the catch, or both. And none of our linemen, with the possible exception of Rivera, blocks well in space.
I don't know how true this is, but I believe I read somewhere that we don't really practice the screen series too much anyway. Now that might come from reports when they were in Oxnard. I would hope we are working on it more these days, especially if we are going to run it in games.