JS Error

After installing the code(supplied by a moderator on this forum) for the image show forward/back arrows, I'm now getting an error-

Webpage error details



Message: 'getElements(...)[...]' is null or not an object
Line: 127
Char: 9
Code: 0
URI: templates/gk_sporter/js/gk_image_show.js


Forget it - I'm removing the custom code and running it in thumbnail mode.
Thanks anyway