failing dimmer switches?

The lighting in my lounge consists of four double wall lights(ie.six lamps) controlled by a dimmer switch. Last year, after years of trouble free use, the dimmer switch failed. I replaced the switch and the first time a bulb blew the new unit failed. I have since fitted a further three switches and all have failed every time a bulb blows. The only change I have made is the use of halogen bulbs as the old iridescent type are not readily available, could this be the problem? I should add I use 6x 60 watt bulbs and the switch units were rated 400W.