It's because the repositories are down, you can add mirror to your list of repositories if you want. http://espejo.freemoe.org/
I added the extras one, because I had to download leafpad.
Today I was trying to get fresh sofware available for my N900 but after refreshing the system says that some catalogues are not valid: maemo.org and maemo Extras. Well, that is a new situation for me as I did nothing and do not know how to solve that. Maybe some temprarily problem on server? Please help.