why can't i use unity web player even i downloaded it on facebook for a game

this is my first post and i use unity for a while already, but there a problem when i play games that need unity on facebook . Before this have no problem with that game , called Under fire . I used to play it but all a sudden i just can't play it anymore . So i download and install it again . Plus the version was 5.1.2F2 that time and even i try now it is still version 5.1.2F2 ...... If anyone can help me . Please Reply as quikly as u can because i want to play Under Fire as soon as possible