Can't apt-get update with multiple releases in sources.list.

[Adam Funk <a24061@yahoo.com>]

I've got Debian stable working on a fairly old machine (P2-350, 4GB
HDD, 128MB RAM, 272MB swap) with the following in
/etc/apt/sources.list:

deb http://security.debian.org/     stable/updates main contrib non-free
deb ftp://ftp.mcc.ac.uk/pub/linux/distributions/Debian/       stable        main contrib non-free
deb ftp://ftp.mcc.ac.uk/pub/linux/distributions/Debian-non-US stable/non-US main contrib non-free


If I add another mirror of stable to the file, it works.  But if I try
to add testing and/or unstable I get the following error:

/root # apt-get  update
Hit http://security.debian.org stable/updates/main Packages
...
Hit ftp://ftp.uk.debian.org testing/non-free Release
Reading Package Lists... Error!
E: Dynamic MMap ran out of room
E: Error occured while processing openbox (NewVersion1)
E: Problem with MergeList /var/lib/apt/lists/ftp.uk.debian.org_debian_dists_testing_main_binary-i386_Packages
E: The package lists or status file could not be parsed or opened.


I've tried several different mirrors and I always get this problem, so
I don't think it's a bad file on one mirror.  Does this really mean my
system doesn't have enough memory to process the package lists?

-- 
Thanks,
Adam