Why can't I break or place blocks in my LAN-enabled world? [duplicate]

Possible Duplicate:
Why can't I destroy or break blocks?

I was playing Minecraft in single-player mode today when I turned on the "Open to LAN" option. I then changed my game mode to "creative" to fly back to my house, but when I turned my game mode back to "survival", I couldn't place anything down or break any blocks!

I've tried re-downloading Minecraft but that didn't help at all. It's just me in this world, so another user couldn't have changed any settings.

Why is this happening and how can I fix it?

Sounds like you put it on to Adventure Mode. Try closing it down and try it again.

Either you are in adventure mode, or you are building/destroying in the spawn, which the game does not like.