Using Add/Remove, you've only checked gnunet-gtk, and not the gnunetd server, which is in the gnunet-server package. You should manually install the gnunet package, it will take care of this.
This is a little messy for you I guess, but the gnunetd server is not strictly needed to use gnunet-gtk, since it can be located on a remote machine. Something to improve, surely.
Using Add/Remove, you've only checked gnunet-gtk, and not the gnunetd server, which is in the gnunet-server package. You should manually install the gnunet package, it will take care of this.
This is a little messy for you I guess, but the gnunetd server is not strictly needed to use gnunet-gtk, since it can be located on a remote machine. Something to improve, surely.