apt-get: no instalation candidat

["Alexander N. Benner" <alex@aleph.christen.net>]

Hi 
trying to upgrade some packages apt-get fails with the msg.

E: Package bigbrother has no instalation candidate

Packages which fail (with this msg):

bigbrother
xplot
xsplay
xwatch

my apt/source.list:

# Use for a local mirror - remove the ftp1 http lines for the bits
# your mirror contains.
# deb file:/your/mirror/here/debian stable main contrib non-free
# See sources.list(5) for more information, especial
# Remember that you can only use http, ftp or file URIs

deb http://non-us.debian.org/debian-non-US unstable non-US
#deb ftp://ftp.eecs.umich.edu/debian potato main contrib non-free
#deb ftp://ftp.eecs.umich.edu/debian slink main contrib non-free

deb http://www.uk.debian.org/debian slink main contrib non-free
deb http://www.uk.debian.org/debian potato main contrib non-free
#deb http://www.de.debian.org/debian potato main contrib non-free

#deb file:/mnt/hdd2/linux.mathematik.tu-darmstadt.de/pub/linux/distributions/debian potato main contrib non-free non-US
#deb file:/mnt/hdd2/linux.mathematik.tu-darmstadt.de/pub/linux/distributions/debian slink main contrib non-free non-US

-- 
Alexander N. Benner

And Jesus answered him, The first of all the commandments is, Hear, O Israel;
The Lord our God is one Lord: And thou shalt love the Lord thy God with all
thy heart, and with all thy soul, and with all thy mind, and with all thy
strength: this is the first commandment. -*- The Bible (Mark 12:29-30)