I'm having trouble connecting to the internet with NetZero on a
telephone modem. I found this message posted in July from a guy with
the same problem:

When trying to connect to Netzero I receive Error 500 "The
Netzero software is unable to connect to the Netzero
network". When attempting to dial in it goes through all
steps OK and when the screen says "Logged on",the modem
disconnects and the modem then redials. I have tried
changing access numbers,modem strings,checked my ID info,
and all other suggestions from Netzero.My laptop logs on
just fine from the same location using the same access
numbers.The only recent software change has been the
addition of McAfee 8.0.But the PC worked fine for about a
week before this started and my laptop dials in with no
problems with McAfee 8.0. Any helpful suggestions will be
appreciated.

He never received any replies to this message. The only difference for
me is that it is a new desktop computer.