They need to redesign their website if they cannot handle the traffic. I say this as I needed to purchase some Manila - KUL tickets at regular price for early June and there was no way I get this done on Air Asia website as it just clunks out. So I purchased on Cebu Pacific instead.
Perhaps a link on front page:
Promo Fares Only --- Home Page
or something.
I think they actually lose their regular flight booking business during these promo deals