A slight problem with keylight

Hi, let's see if you can help me with this. I'm editing various r3d files and I'm having problems when it comes to remove a green screen. Basically when I import them they look a bit dark by themselves. Example:

Now this is how it looks when I apply keylight, without touching enything else:

The problem is, that no matter how hard I try, the result looks terrible:

I honestly don't know what I'm missing, I've never had this problem since I always got a perfect result using keylight. I don't know if it's because of the r3d files. Any ideas?

Thanks in advance.