Comment 6 for bug 659632

I believe I have the same issue.
We have been deploying Ubuntu by pointing the Ubuntu mirror to an internal mirror with a preseed file. This has been working for us since Ubuntu 7.04. I use the same preseed file and just change the directory. Now it's trying to install from gb.archive.ubuntu.com. The d-i installer stops with the error:
Bad archive mirror. An error has been detected while trying to use the specified Ubuntu archive mirror.

my preseed file mirror section:
d-i mirror/country string manual
d-i mirror/http/hostname string {our internal http server}
d-i mirror/http/directory string /ubuntu/1010-64
d-i mirror/suite string maverick
d-i mirror/http/proxy string