Problem with the Landscape Editor

[SkelApe]

Hey everyone, i'm back! I'm having a little problem with the Landscape editor. At present i'm trying to release three of the sandbox maps i've made, but the editor doesn't want to open one of the landscapes, and closes when I try. While i haven't opened the landscape for a while, i have changed nothing about it, and i'm pretty certain it worked last time. What's more, the land crashes the game when I try to use it. Can anyone offer some help?

Thanks