[CentOS] CentOS-3.3 to 3.5 Upgrade Error

Sun Aug 7 16:56:53 UTC 2005
Support <support at ev-theol.uni-bonn.de>

Thank you for the advice to update!
Problem is that i get the following error message:

Gathering header information file(s) from server(s)
Server: CentOS-3.3 - Addons
Server: CentOS-3.3 - Base
Server: CentOS-3.3 - Extras
retrygrab() failed for:
http://mirror.centos.org/centos-3/3.5/extras/i386/headers/header.info
Executing failover method
failover: out of servers to try
Error getting file 
http://mirror.centos.org/centos-3/3.5/extras/i386/headers/header.info
[Errno 4] IOError: HTTP Error 404: Not Found

Somebody knows what´s going wrong? tia!