I have found a great theme called Crystalised but it has very busy wallpaper that makes the Active Standy details illegible!

I have selected new wallpaper but I can still see a 1pixel (maybe) line of the theme wallpaper down each side.

What causes this and how can I get rid of it?

Thanks

Go into the Themes menu. Select 'Options'. and then 'Edit'. Make sure the wallpaper is set to 'User Defined' and not 'Default'.