"The following packages have been kept back"

[matlads@techmuk.ac.ug]

Hi everyone,

I tried  to move from stable to testing yesterday. I edited my sources.list
and changed all occurances of 'stable' to 'testing'. I then run  the
following: 
 fot2:~#apt-get update
 fot2:~#apt-get dist-upgrade

It upgraded only a few of the packages and 'kept' back the rest.

i rerun the above commands, to see if I could get the rest to also be
upgraded and I got the following output:

 fot2:~# apt-get dist-upgrade
 Reading Package Lists... Done
 Building Dependency Tree... Done
 Calculating Upgrade... Done
 The following packages have been kept back
   aalib1 abbrowser adduser ae aktion alien apache apache-common apt apt-move
   base-config base-passwd bash bc bin86 bind binutils bison bsdmainutils
   bsdutils bzip2 console-data console-tools console-tools-libs cpio cpp cron
   dc debconf debhelper debianutils dlint dnsutils dosemu dpkg dpkg-dev dwww
   e2fsprogs ed eject elvis-tiny esound exim fdutils fetchmail fetchmailconf
   file fileutils findutils finger fingerd fortune-mod freetype2 gnupg
   kdebase-crypto kdelibs3-crypto libssl09 lynx-ssl openssl postgresql
   postgresql-client ssh
 0 packages upgraded, 0 newly installed, 0 to remove and 62 not upgraded.

What is going on, and why can't apt-get upgrade the remaining 62 packages?
How do I get it to upgrade them?

Martin.
-- 
$file /usr/bin/file
/usr/bin/file: unknown file type (edit /etc/magic, or read magic(5))