I take your statement to mean that you have two '/etc/network/interfaces' files. If that is the case and there is information statically configured in them for your network interface this will not work with network manager. For network manager to manage your interface there should only be lines like this:
auto eth0 iface eth0 inet dhcp in it. -- Sees wireless networks but wont connect https://launchpad.net/bugs/98612 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
