Hi,
due to serious disk space limitations on mirror hosts, the non-LTS
architectures of the Squeeze release will get removed from the mirror
network starting today. That is, only Squeeze i386/amd64 continue to be
hosted on the normal mirrors.
The data is, of course, not lost - the whole of Squeeze is syncing
to archive.debian.org, so if you still need it for any of the non-LTS
architectures you will be able to get it from there.[1]
This does not (yet) affect other Squeeze suites, like backports, but
they will follow soonish.
[1] Keep in mind that they have no security support at all!