Hi
Ok. Lets try to help both of You
I'm really bad with javascript but will tell You what to check.
First of all. Please upgrade GK Image Show module (files are inside the Photoslde GK3 pack). There were a small bug with missing letter in function name which was fixed in the module but probobly weren't removed from the quickstart.
Secondly please try to disable/enable mootools plugin and see if this helped. If not please try to do the same with disabling/enabling mootools and "Use script" in modules Advanced Parameters.
That's what I do when got such problem