hi,days ago i played a live chess game http://www.chess.com/livechess/game.html?id=102211357. As you can see move no. 41-87 there was a several perpetuals and it should be atlast drawn 20 times!But the system never take it so i play on and due to time pre. my opponent blundered.I said sorry to my opponent but I really want to know why this happened.Any clue from any one??Thanking in advanced

The system never claims it on it's own, neither would an arbitrer in otb chess, one of the players has to claim the draw once the treefold repetition occur.

thanks tricklev

I agree to the solution, because I have also experienced it.

You must claim any draw by threefold repetition of position or the 50-move rule.  There is no such thing as a draw by perpetual check under the rules:  players subject to perpetual check usually  just recognize that it must inevitably result in one of the legal ways to draw, and agree to it.