See my last post to JHavard. You are introducing here the Christian concept of "messiah". There is nothing sinful or contrary to the commandments for someone to believe that he is the messiah (as I defined it above). Even if he is wrong. Throughout history there have been many messianic claimants. They may have been wrong. They may have failed. But they didn't sin in proclaiming themselves as such.
There is a Jewish tradition that in every generation, there is a man who has the potential to be the messiah. The only way we'll know we've found the right guy is when he has fulfilled the prophecies. Until he has done that, he is, at best, a candidate.
Hey, has anybody keyed Steven in on this yet? He's never been a big fan of tradition. -)