Here's my complete one, for comparison sake, all fully operating:
# See sources.list(5) for more information, especialy
# This file may be edited by the MEPIS System Center
# Do not modify the comments manually!
# Change sources only in the section at the end of this file!
# Primary
deb
ftp://ftp.us.debian.org/debian/ unstable main contrib non-free
#deb-src
ftp://ftp.us.debian.org/debian/ unstable main contrib non-free
deb
ftp://ftp.us.debian.org/debian/ testing main contrib non-free
#deb-src
ftp://ftp.us.debian.org/debian/ testing main contrib non-free
deb
ftp://ftp.us.debian.org/debian/ stable main contrib non-free
#deb-src
ftp://ftp.us.debian.org/debian/ stable main contrib non-free
# non-us
deb
ftp://non-us.debian.org/debian-non-US unstable/non-US main contrib non-free
#deb-src
ftp://non-us.debian.org/debian-non-US unstable/non-US main contrib non-free
deb
ftp://non-us.debian.org/debian-non-US testing/non-US main contrib non-free
#deb-src
ftp://non-us.debian.org/debian-non-US testing/non-US main contrib non-free
deb
ftp://non-us.debian.org/debian-non-US stable/non-US main contrib non-free
#deb-src
ftp://non-us.debian.org/debian-non-US stable/non-US main contrib non-free
# security
deb
http://security.debian.org/ woody/updates main contrib non-free
#deb-src
http://security.debian.org/ woody/updates main contrib non-free
# MEPIS cds
#deb file:/mnt/cdrom unstable main
#deb file:/mnt/cdrom testing main
#deb file:/mnt/cdrom stable main
# MEPIS pool - specific packages available on-line
deb
http://2005.mepis.org/mepis unstable main
# DO NOT EDIT ABOVE THIS LINE
# mplayer
deb
ftp://ftp.nerim.net/debian-marillat/ unstable main
#deb-src
ftp://ftp.nerim.net/debian-marillat/ unstable main
deb
ftp://ftp.nerim.net/debian-marillat/ testing main
#deb-src
ftp://ftp.nerim.net/debian-marillat/ testing main
deb
ftp://ftp.nerim.net/debian-marillat/ stable main
#deb-src
ftp://ftp.nerim.net/debian-marillat/ stable main
What happens if you put a # in front of deb-src, like I have in my list?