"No mirrors remaining, giving up". when trying to update(minor or version )

[paljibus]

   Helo gurus,
   my system is:
   FreeBSD cvs2.abvent.fr 7.0-STABLE-200806 FreeBSD 7.0-STABLE-200806 #0:
   Mon Jun  2 18:36:08 UTC 2008
   [1]root at driscoll.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC  amd64
   cvs2# 
   I installed that half-year version of FreeBSD 7, and I get in trouble
   when updating:
   it says:
   cvs2# freebsd-update fetch
   Looking up update.FreeBSD.org mirrors... 2 mirrors found.
   Fetching public key from update1.FreeBSD.org... failed.
   Fetching public key from update2.FreeBSD.org... failed.
   No mirrors remaining, giving up.
   cvs2# 
   It seems my key is bad, because I installed a 7+ version? where is my
   key?
   any idea?

References

   1. mailto:root at driscoll.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC