On Mon, Jun 19, 2017 at 08:29:56PM -0400, Leo Famulari wrote:
> Starting download of /gnu/store/x8x9s119g1xhdxrzaka35lx4p45qd3vg-linux-libre-4.4.47-gnu.tar.xz
> From ftp://alpha.gnu.org/gnu/guix/mirror/linux-libre-4.4.47-gnu.tar.xz...
> ERROR: Throw to key `ftp-error' with args `(#<input-output: socket 12> "RETR linux-libre-4.4.47-gnu.tar.xz" 550 "Failed to open file.\r")'.

I guess somebody with a copy of this file needs to add it to 
<ftp://alpha.gnu.org/gnu/guix/mirror/>.