Gpg error when trying to update

[onyx666]

I did an upgrade today About 180 packages where upgraded. Now i try to update and get the following error
Anyone know hoe to solve?

Last login: Mon Sep 14 20:34:22 2015 from 10.0.0.40
xbian@xbian ~ $ sudo apt-get update
[sudo] password for xbian:
Get:1 http://http.debian.net stable Release.gpg [2,373 B]
Hit http://http.debian.net stable Release
Hit http://www.mirrorservice.org/sites/apt.xbian.org/ stable Release.gpg
Hit http://www.mirrorservice.org/sites/apt.xbian.org/ stable Release
Ign http://http.debian.net stable Release
Hit http://www.mirrorservice.org/sites/apt.xbian.org/ stable/main armhf Packages
Hit http://http.debian.net stable/main armhf Packages
Hit http://http.debian.net stable/non-free armhf Packages
Hit http://www.mirrorservice.org/sites/apt.xbian.org/ stable/rpi-jessie armhf Packages
Hit http://http.debian.net stable/main Translation-en
Hit http://http.debian.net stable/non-free Translation-en
Ign http://http.debian.net stable/main Translation-en_US
Ign http://http.debian.net stable/non-free Translation-en_US
Ign http://www.mirrorservice.org/sites/apt.xbian.org/ stable/main Translation-en_US
Ign http://www.mirrorservice.org/sites/apt.xbian.org/ stable/main Translation-en
Ign http://www.mirrorservice.org/sites/apt.xbian.org/ stable/rpi-jessie Translation-en_US
Ign http://www.mirrorservice.org/sites/apt.xbian.org/ stable/rpi-jessie Translation-en
Fetched 2,373 B in 25s (93 B/s)
Reading package lists... Done
W: GPG error: http://http.debian.net stable Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY 7638D0442B90D010 NO_PUBKEY CBF8D6FD518E17E1
xbian@xbian ~ $