What's going on? Is this a bug? Please help!

I’ve been working on this for a while now, and I rendered it one time, and this strange thing happened. I can’t figure out how to make it go away. Please help!

isn’t that obvious?
this is an alien-armada, going to land!

okay, seriously: no idea.
is this an angMap? sky-texture?

lol…it’s just a plane with a cloud texture on it (Nor map).