I started the Laid to Rest quest in Morthal. What happened to me is not what is written in the strategy guide. Two things are different. I followed the marker to the cemetery after dark. I killed the vampire there. I was not able to open the child's coffin and the marker is staying on it. I get the prompt to open, but clicking does nothing. I went to Alva's house right after that, still night time. I was ready to kill me another vampire. No one was home at Alva's. I got her journal and took it to the Jarl. I stopped playing for the evening saving the game in front of an angry mob with torches and pitchforks ready to kill the big bad vampire dude. I hope there are no more bugs. After 18 hours of play, this is the only bug I found (unless killing a chicken is not a crime).

apparently their are quite a few people having issues with this quest, especially concerning the girl in the coffin and not being able to interact with it. Hopefully this issue is fixed and patch along with the many others, which I'm surprised you haven't run into thus far -.-.