New user mail registration error

I download the most current build on Dec. 04,2009. Made a fresh installation.

When I use email registration the the software sends a link to the new user, along with the user name and password. Good so far.

...com/index.php/register.php?activate=f0b43d41bb09427f2e2bd91........

The problem is the link. When you click on the link the browser states something to the effect the that the redirection is a circular redirection which can not be displayed.

The URL shows
example ...com/index.php/news.php
or ...co,/index.php/articules.php
depending on the Site opening page:
I even tried changing Admin control panel>setting>main>Site opening page:
without an php page (NEVER DO THAT!)

So the link won't work and the new user can't log in.
Their information is in the new_user MySQL DB.

I looked through the forum but couldn't find any posts.
Do you have any suggestion?

Tim
timlkane@yahoo.com