Rename function not working

[eluser]reyntjensw[/eluser]
I'm trying to rename a file that's in my images folder. So I'm using rename

Code:

rename(realpath("../images/sky2.jpg"),realpath("../images/sky3.jpg"));

The file exists in my folder and has all permissions, (I did a chmod 777).
I'm also able to upload images in that folder so the folder (I think) isn't the problem.

Anyone with ideas?

Thanks