sources 404

[spider_0k]

I have a Powerbook G4 12". I have installed Lucid 10.04, including updates without problem.
I am attempting to upgrade to Maverick, online because it is (I thought) straightforward. I am running into this problem. Update Manager fails to update the files in Lucid 10.04. The Internet access is fine but it fails to fetch from repository (404). I haven't changed any setting but since installation. I realized the Update Manager is not working. I tried different servers, cn, tw, us, uk and distributions 10.04, 10,10, 11.04, the results were the same.
Additionally to make things clearer I have simplified my sources.list:-

################################################## ###########
################### OFFICIAL UBUNTU REPOS ###################
################################################## ###########

###### Ubuntu Main Repos
deb http://cn.archive.ubuntu.com/ubuntu/ lucid main restricted universe multiverse

###### Ubuntu Update Repos
deb http://cn.archive.ubuntu.com/ubuntu/ lucid-security main restricted universe multiverse
deb http://cn.archive.ubuntu.com/ubuntu/ lucid-updates main restricted universe multiverse
deb http://cn.archive.ubuntu.com/ubuntu/ lucid-proposed main restricted universe multiverse
deb http://cn.archive.ubuntu.com/ubuntu/ lucid-backports main restricted universe multiverse

All other internet functions are fine.
Thanks in advance for your help
Philip