hi there im a complete newbie using zencart, i just installed this addon which is excellent but i have a problem

i have added additional pics in the format like this
abc.jpg
abc_01.jpg
abc_01.jpg
....
....

now when i clicked the main pic it display in lightbox no problem, it shows that its the 1 of 7 pics, and all next, close, etc buttons, but when i click next to view the 2nd pic, it shows the loading icon but doesnt go to the 2nd pic at all. if i click direct on the additional pic instead of the main one, lightbox comes up but doesnt show pic at all. what have i done wrong or need doing? i have rename template name and followed the instruction already, thanks very much for your help

Wil