Erro in update of RHEL 5.4

[Eduardo Herrera Leiva]

HI
 I need update of RHEL 5.4 but yum displayed the error:

Total download size: 85 M
Is this ok [y/N]: y
Downloading Packages:


Error Downloading Packages:
  libstdc++-4.1.2-46.el5_4.2.x86_64: certificate verify failed
  krb5-workstation-1.6.1-36.el5_4.1.x86_64: certificate verify failed
  krb5-devel-1.6.1-36.el5_4.1.x86_64: certificate verify failed
  dbus-libs-1.1.2-12.el5_4.1.x86_64: certificate verify failed
  tzdata-2009u-1.el5.noarch: certificate verify failed
...
...
..
..
...

 earlier, I had no problems

Thank and regards

-- 
_____________________________________
Eduardo A. Herrera Leiva
Administrador de Sistemas
SubDirección de Operación y Plataforma
Dirección de Informática
Pontificia Universidad Católica de Chile
Teléfono: 56 2 354 1369