Sony Vegas Movie Studio HD 9.0 post rendering audio lag help!?

I have Sony Vegas Movie Studio HD 9.0. I am editing the wedding I did with 2 different cameras. Everything turned out great. When I ran it through the Vegas program, everything was good. I rendered it and saved it to my hard drive in a .wma format. I double clicked and started to watch it. When it came time for the priest to talk, I saw that the audio was out of sync with the video. I read that maybe it was the format that it was in, so I tried a .mp4 format. Still audio was lagging. Another thing is, is that on some frames it was perfect, but 90% of the film, the audio is lagging. When i watched it with the Vegas program it worked fine. What caused the lag during rendering?