Preexisting single player world to a server

I am a Youtuber who is trying to get my existing SSP into a SMP in order to do a 3rd person time-lapse (Lan doesn't work for some reason). I did the quick and dirty free minecraft.net server. Everything runs great both my machines can access the server if it is set up with a brand new world, that's all the good news. after attempting to move my SSP world over neither machine can access the server and the bars have an X with Old next to it. I have tried simply moving the files into the world folder, tried replacing level.old files to make it think its a new world. Any help is much appreciated.