problem apt-get'ing debian source packages

[Griffith Feeney]

I've used apt-get for installing binary packages for some time and it works
like a dream, but I'm having trouble getting it to install source packages.
I've uncommented the lines in /etc/apt/sources.list, but when I do, e.g.,
"apt-get source gcc" I get the message

"Could not open file
/var/stat/apt/lists/non-us.debian.org_debian-non-US_lists_stable_non-US_sour
ce_Sources - open (2 No such file or directory)"

I've been through the documentation but remain unclear why I'm getting this
message or what to do about it. Any clues? Thanks!