Why do I get "fatal: git status --porcelain failed"?

This is a huge pain in the bum. I've got this a few times before and I don't understand why. 5 mins ago the repo was fine and working, I move some files around (which is all cool and all) and git poops its pants. Any idea why this happens? How can I fix it apart from cloning the repo, moving the files, etc...

What is git status porcelain?

Porcelain Format Version 1 Version 1 porcelain format is similar to the short format, but is guaranteed not to change in a backwards-incompatible way between Git versions or based on user configuration. This makes it ideal for parsing by scripts.

Oh dear I'm such a fail. It looks like the problem stems from Flash Builder copying over other .git repos into sub folders. The answer is to remove all .git folders that aren't the repo's one.

I ran into this error because of a corrupted/not properly initialized submodule (with its own .git subfolder). I temporarily deleted the submodules folder and used git init in the main project's root. Fixed the problem for me.