Please provide some additional info:
  * rsync server config - if rsync is running under xinetd, then include
      /etc/xinetd.conf, and /etc/xinetd.d/rsync
  * relevant entries from /var/log/messages on rsync server
  * rsync command used on client to connect to server
  * version of rsync client
  * any other relevant info

Here are the config files you asked for. I do not know what command the
client was using since I do not have access to it. I think it might be a
variant of the following:

rsync -vrlptog --delete stage.mozilla.org::mozilla-ftp /home/ftp/pub

Note that stage is a cname to hemosaur.

/etc/xinetd.d/rsync

# default: off
# description: The rsync server is a good addition to am ftp server, as it \
#       allows crc checksumming etc.
service rsync
{
        disable = no
        socket_type     = stream
        wait            = no
        user            = root
        server          = /usr/bin/rsync
        server_args     = --daemon
#       log_on_failure  += USERID
}

/etc/rsyncd.conf

log file = /var/log/rsync
# this is a comment
[mozilla-ftp]
        path=/home/ftp/pub/
        comment=Mozilla FTP

Adding the following to the server rsyncd.conf files makes this error
go away:

log file = /var/log/rsync
# this is a comment
[mozilla-ftp]
        uid=root
        gid=root
        path=/home/ftp/pub/
        comment=Mozilla FTP

So the question is, why aren't these options required for the rsync that is 
shipped with Red Hat Linux 7.3 versus the one shipped in Red Hat Advanced Server
version 2.1?

the problem turned out to be permissions on files and directories being
transferred when using anonymous rsync, which uses modules defined on the server
in /etc/rsyncd.conf.

'man rsyncd.conf' on rsync-2.4.6-13 says this for uid:

       uid    The "uid" option specifies the user name or user id
              that  file transfers to and from that module should
              take place as when the daemon was run as  root.  In
              combination  with  the "gid" option this determines
              what file permissions are available. The default is
              the user "nobody".

Note that if the uid is not specified in the module, that the default uid is
"nobody".  The code does a setuid to the uid specified (or default 'nobody') in
the module before it does the transfers.  So if the code does a setuid to
'nobody', then it will fail to open files and directories that don't give user
'nobody'(and group 'nobody') permission to read them.

In this case, rsync is failing with an abnormal termination because of
permissions problems when opening *directories* that don't give read access to
the rsync uid.  *Files* that don't give permissions to that uid cause an error
to be displayed, but do not cause abnormal termination.

rsync-2.5.5-4 which ships with Red Hat Linux 9 does not abnormally
terminate when encountering directories that don't give read permissions
to the rsync uid - permissions error messages are displayed for each
file and directory that couldn't be read, but those errors do not cause
rsync to abnormally terminate.

The solution for 'daemon' users of rsync-2.4.6-13, and 'daemon' users
of all subsequent rsync versions, is to specify in each /etc/rsyncd.conf
module, as directed by the rsyncd.conf manpage, "the user name or user
id that file transfers to and from that module should take place as
when the daemon was run as root".  Like the manpage says, add 'uid=some_user'
and 'gid=some_group' to each module.