freebsd-update no mirrors?

[Chris Whitehouse]

c400# uname -a
FreeBSD c400 9.0-RELEASE FreeBSD 9.0-RELEASE #0: Tue Jan  3 07:15:25 UTC 
2012     root at obrian.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC  i386

Following the handbook:

c400# freebsd-update -r 9-STABLE upgrade
Looking up update.FreeBSD.org mirrors... 4 mirrors found.
Fetching metadata signature for 9.0-RELEASE from update4.FreeBSD.org... 
done.
Fetching metadata index... done.
Inspecting system... done.

The following components of FreeBSD seem to be installed:
kernel/generic src/src world/base world/doc world/games

The following components of FreeBSD do not seem to be installed:

Does this look reasonable (y/n)? y

Fetching metadata signature for 9-STABLE from update4.FreeBSD.org... failed.
Fetching metadata signature for 9-STABLE from update2.FreeBSD.org... failed.
Fetching metadata signature for 9-STABLE from update5.FreeBSD.org... failed.
Fetching metadata signature for 9-STABLE from update3.FreeBSD.org... failed.
No mirrors remaining, giving up.

In case I had got the CVS tag wrong I also tried 9.0-STABLE with the 
same results.

I haven't changed freebsd-update.conf

Am I doing something wrong? This is the first time I've used 
freebsd-update, except that just now I apparently successfully did 
freebsd-update fetch and freebsd-update install on this machine.

Thanks

Chris