The "right" way of doing backgrounds in C2?

I'm importing png images to the background but they get a fine line in the transparent part of the image when I use them as tiled background, has anyone had it?

I'm importing png images to the background but they get a fine line in the transparent part of the image when I use them as tiled background, has anyone had it?

I don't think I encountered the problem before, but showing a screenshot of the problem might get you help faster.