For future reference, don't always just commit to running apt-get upgrade. That can cause problems (like certain packages that you can install, getting downgraded to stock Nokia ones, or upgraded to more recent versions that you might not want, if a more recent version is in the repos you have enabled. [If they aren't pinned]), which is usually not an issue, but it's something people should take the time to warn about when writing up advice to run "apt-get upgrade".

ANYWAY, the other thing is, if you've never installed the CSSU, this won't work for you - you'll have to manually add the CSSU repository information in Hildon Application Manager (or through the command line if you know where to do that). The repo info is:
URL: http://repository.maemo.org/community-testing/
distribution: fremantle
components: free non-free

(Bear in mind this might not be the safest thing to do the very first time you run it. The initial install is a bit different than apt-get just upgrading available packages as far as I know.)