I tested pasting a different mood theme url into the custom mood theme editor - one which was a .jpg file and not a .png.

That loads just fine. Something about the image being a .png file results in an error image from photobucket saying that the image has been deleted or moved. Which is hasn't.

I'm taking this to mean that the console doesn't currently 'read' png's - or that there's some disconnect from Photobucket.

Sigh.

Thank you for your detailed comment that did help me check my way through everything prior to realising this.