Social Slider Icons seem to be missing on install

Hi,
I've installed the module on my test site but there seem to be no icons for the standard social sites (or at least they are not displaying). When I hover over any of the boxes the option to follow on particular media displays and the link works - but without the icon it makes little sense.
I've attached a screenshot below.
When I look in the folder /test/media/mod_social_slider/icons it shows only three files:
index.html
Sprite-black.png
Sprite-white.png
From other comments in the forum I assume that this folder should contain the icons for the standard sites. Have I installed the module incorrectly and is there a step I've missed out.
Many thanks for any guidance you can offer.

Brilliant support - problem now resolved. It was the error in the configuration.php file. Thank you so much for your very fast and efficient response.