Chess Related

I am looking for a php expert, I have a website devoted to chess and I am using a chess engine (one php file) the checks the moves and verifies the legality of those moves. The problem I am having is the code need to be reviewed because it appears to lose track of the chess position and ends the games (declares a winner just on checks instaed of checkmate). So I need someone who knows chess and can correct the php code to make sure it does exacly what is is supposed to do regarding checking the moves correctly and declaring mate when it really is mate and not just check. The site and mor information will be provided to the succesful person. Thanks