Trying to register a system

[Margaret Doll]

We just installed a RedHat 5.3 system successfully using our  
installation number.

I can see the new subscriptions listed on my accounts https://www.redhat.com/wapps/support/protected/subscriptions.html 
  page.
I also have nine subscriptions and eight computers registered.

When I go to register our new system using pup,  pup says  that the  
installation
number that I have provided is invalid.  It suggests that I try the  
option listed on
the 'Access a Subscription' screen.

I have tried entering the installation number repeatedly, even cutting  
and pasting it into the form.
I have tried entering the installation number with and without the  
hyphens.

And where is the 'Access a Subscription' screen?

How do I get the updates working?