E-shop with error

We bought a webshop, and now with some altering of the design the company that we bought if from is not able to help me out with what might be wrong since they feel that I changed it to much.:(
The original sample of the shop is at: MidiCart Java WebShop - Demobutik 1

my shop is at: MidiCart Java Webshop

I figured that I would try to do some test shopping, but that's when it hit stop.. something is wrong. the protein.html page is working when I put it in their unaltered sample, but I it woun't work in the altered version.
What is it that I've done wrong?:confused:

Please excuse my written english, it's not as good as it use to be

Please help me

Moving your thread to the Advanced section.. unless someone has a better place for it.