Why won't any WordPress themes work?

I was looking on here http://www.1stwebdesigner.com/wordpress/… for free wordpress themes and I found a few that I liked when I tried to upload them and install them and none of them worked! Everytime I upload one I get an error like this Fatal error: require() [function.require]: Failed opening required (then my domain name) etc.
Why does this keep happening? I contacted the hosting and they said its something with the themes not there hosting.