Black border in the background in render

Not sure what is going on here, can anyone illuminate me?



Forum search is your friend: This has been asked a gazillion times before…
You have stacked more transparent planes behind each other than the ray depth for transparent rays is set to, so the ray is terminated prematurely and comes back as black.

https://dl.dropboxusercontent.com/u/27650383/31-12-2016%2017-18-12.png

My apologies. I didn’t know what to search for. Thanks for the help!