Apt-Get "sources.list needs at least 1 source-URI" error when building dependecies for Xen

What i'm trying to do is install Xen in a test environment, now I am trying to run the:

apt-get build-dep xen-3.3

command, but it keep throwing a error which literally translated from dutch (installed the debian OS in Dutch) say's:

E: your sourcelist (/etc/apt/sources.list) has to contain at least 1 source-URI

I've googled it but I can't seem to find a definitive solid answer on how to fix this.

By default a source-URI (read man page of apt-get) states it needs to be something along the lines of

deb ftp://ftp.debian.org/debian stable contrib

Now I've got 2 HTTP sources (default Debian ones) up & running so far and they've been working flawlessly for the better part of a few days now. Only now its starting to act up.

Anyone able to help me out ?

Much obliged !