I editied the displayed page source to remove the /DesktopModules/ part of the link and the icon displayed OK.
I am trying to investigate where this error may lie, given that it is a bought skin that is not easy.
I am technical but not DNN technical. (My expertise is 1970s/80s based!). However I am confortable making tweaks if I know where to go to.
It is obvious to me that some bit of code somewhere contains the wrong definition for the source of standard icons. Any hints? Or could it be anywhere?
It is of course a small issue but it is good to have things working correctly. Thanks for your interest.