freebsd-update to 6.4-RELEASE doesn't work

[Thomas Krause]

Dear list,
I cannot upgrade my 6.3-RELEASE-p7/i386 to 6.4-RELEASE with 
freebsd-update. I have run:

# freebsd-update upgrade -r 6.4-RELEASE

and then

  # freebsd-update install
No updates are available to install.
Run '/usr/sbin/freebsd-update fetch' first.

any ideas?
(btw: I've successful updated 6.3REL/amd64 to 6.4-REL)

Best regards,
Thomas.