Minecraft singleplayer Server Closed?

I was playing Minecraft on singleplayer then i decided to adventure and get away from my house. After i decided to go back it kicked me out saying "Server Closed", now when I try to join again it doesn't let me. I was only using 1.7.9 with optifine. Please help anyone i just got the world and have gotten pretty far in it if someone can tell me how to fix it I will be so happy.