Altium High Speed Design Rule (Trace Length)

Hi, I use Altium designer to auto-route my board, I set the Max Length - High Speed Design Rule from Design>>Rules Menu. (Max Length = 38.1mm) When the auto-routing is done, it seems that the Max Length rule i set was not observed, i've tried to re-route many times but i got the same result. It seems that the rule i set is not 'active' at all, any ideas.

Thanks.