[OS X TeX] problem with TeX Live Utility

[juan tolosa]

For the past few days, when TeX Live Utilitly attempts to perform the daily updates, 
I am getting the following error message:

Unable to find a valid update server.
Either a network problem exists or the TeX Live version
of the server does not match. If this problem persists on further
attemps, you may need to try a different repository.

In the past, this problem was an indication that I was not connected to the internet. 
Now, however, I am connected all right, but I am still getting the same message every time.

I am not an expert in the technical part, I am just a happy (and very grateful) user
of this wonderful TeX platform. All the set up for TeX Shop and for the TeX Live Utility
were done automatically when I first installed MaC TeX.
Just in case, I did try the "check for updates," with TeXShop, 
and I get the answer "TeXShop 3.18 is currently the newest version available."

When TeX Live tries to get the updates on my end, it connects to

http://mirror.ctan.org/systems/texlive/tlnet

Any suggestions will be very welcome.
Thanks,
                             Juan