Gradient banding

[zooropa]

Hi, I am trying to post process a render in PS.

I followed the tutorial from Esben, but this time I can not get rid the "stripes" that my gradient leaves on my render.

I am trying to apply a gradient and overlay it in order to enhance the depth of the render. I applied this effect in other opportunities. I do not recall this happening before. Same computer. I am wondering if it could be a problem with the file type ?

Please find the image attached,

Regards