If it happens once, it could have been something stuck in the door.
If it happens often, then you need a new vacuum pump. There is some sort of lock-out that disables the pump if it hasn't seen the microswitch in a certain amount of time.
This is a common problem with these cars. Like I saw in a previous post, keep following the Reset procedure until it annoys the heck out of you, then its time to replace the pump.
BTW, mine's been doing the same thing for some time. Haven't broken down to get a new pump yet...mucho $$$ up here in Canada.