upgrading to 7.1-rc2 doesn't work


When i try to update to 7.1-rc2 this happens :

tamara# freebsd-update upgrade -r 7.1-rc2
Looking up update.FreeBSD.org mirrors... 1 mirrors found.
Fetching metadata signature for 7.0-RELEASE from update1.FreeBSD.org... done.
Fetching metadata index... done.
Inspecting system... done.

The following components of FreeBSD seem to be installed:
kernel/generic src/base src/bin src/cddl src/compat src/contrib
src/crypto src/etc src/games src/gnu src/include src/krb5 src/lib
src/libexec src/release src/rescue src/sbin src/secure src/share src/sys
src/tools src/ubin src/usbin world/base world/catpages world/dict
world/doc world/games world/info world/lib32 world/manpages

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

Does this look reasonable (y/n)? y

Fetching metadata signature for 7.1-rc2 from update1.FreeBSD.org... failed.
No mirrors remaining, giving up.

What is going wrong here ?