Problems with RHN repository in RHEL Desktop v.5 x86_86

Good night mates,

I'm currently unable to update or install any packages from my system
(RHEL Desktop v. 5 x86_64) because of this error:

[user@machine ~]# yum check-update
Loaded plugins: rhnplugin, security
rhel-x86_64-client-5                                     | 1.4 kB     00:00
rhel-x86_64-client-5/primary                             |   10 B     00:00
rhel-x86_64-client-5/primary                             |   10 B     00:00
rhel-x86_64-client-5/primary                             |   10 B     00:00
rhel-x86_64-client-5/primary                             |   10 B     00:00
Error: failed to retrieve
repodata/4d9b8fc1779a8bd59019ff7a315439c417ffd402-primary.xml.gz from
rhel-x86_64-client-5
error was [Errno -1] Metadata file does not match checksum

Have you guys ever faced this problem, and possibly know a solution?

I've tried commands like...

yum clean metadata
yum clean all
rm -rf /var/cache/yum/*
rm -rf /var/spool/up2date/loginAuth.pkl

... but with no success, unfortunately.

Thanks for your cooperation.

Kind regards,

Bruno Martins