I have a single switch that is connected to a double switch. The single switch went bad and caused the double switch to stop working. I replaced the single switch that works but the double switch still did not work so I replaced the double switch and it still does not work. What did I do wrong?

Are you saying this is a 3 way switch? Two switches in different locations that can each turn on a common light. http://www.youtube.com/watch?v=7smZbyBSVTg