dpkg error when running apt-get upgrade.

[MarvinTheRobot]

hi there, i'm still getting errors while running apt-get update (i have the newest xbian package installed on a fresh SD card...)

Code:

Hit http://archive.raspberrypi.org wheezy Release.gpg
Get:1 http://download.telldus.com stable Release.gpg [198 B]
Hit http://mirrordirector.raspbian.org wheezy Release.gpg                  
Hit http://archive.raspberrypi.org wheezy Release
Hit http://mirrordirector.raspbian.org wheezy Release
Get:2 http://download.telldus.com stable Release [2,367 B]
Hit http://archive.raspberrypi.org wheezy/main armhf Packages
Hit http://mirrordirector.raspbian.org wheezy/main armhf Packages              
Get:3 http://xbian.dehakkelaar.nl/ wheezy Release.gpg [3,639 B]                
Hit http://mirrordirector.raspbian.org wheezy/contrib armhf Packages          
Hit http://mirrordirector.raspbian.org wheezy/non-free armhf Packages        
Get:4 http://xbian.dehakkelaar.nl/ wheezy Release [3,639 B]          
Hit http://mirrordirector.raspbian.org wheezy/rpi armhf Packages              
Err mirror://apt.xbian.org wheezy Release              

Ign http://archive.raspberrypi.org wheezy/main Translation-en_US        
Ign http://archive.raspberrypi.org wheezy/main Translation-en
Ign http://mirrordirector.raspbian.org wheezy/contrib Translation-en_US
Ign http://mirrordirector.raspbian.org wheezy/contrib Translation-en
Ign http://mirrordirector.raspbian.org wheezy/main Translation-en_US
Ign http://mirrordirector.raspbian.org wheezy/main Translation-en
Ign http://mirrordirector.raspbian.org wheezy/non-free Translation-en_US
Ign http://mirrordirector.raspbian.org wheezy/non-free Translation-en
Ign http://mirrordirector.raspbian.org wheezy/rpi Translation-en_US
Ign http://mirrordirector.raspbian.org wheezy/rpi Translation-en
Fetched 6,205 B in 4s (1,306 B/s)
Reading package lists... Done
W: A error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: mirror://apt.xbian.org wheezy Release: The following signatures were invalid: NODATA 1 NODATA 2

any help would be really appreciated