In the page that doesn't work you are including jQuery twice.
Once in line 4
and once in line 94:
Remove the second version and this will solve your problem.
BTW, the reason you are seeing the error you posted is that this:
So, within this file, you first load jQuery, then you load the lightbox plugin which adds the lightbox method to the $ function.
Then you load the second version of jQuery, which replaces the $ function - and the lightbox method with it.