From everything I've researched and tried, it appears that my named.conf is configured correctly, including the allow-transfer section.

Here is a sample of the errors. It is only happening with a couple of my secondary servers, but it is happening for every zone for those servers that are failing. One of the servers is attempting IXFR, the other AXFR. The result is the same:

18-Mar-2011 14:27:51.372 security: error: client 84.234.24.90#59208: zone transfer 'juansgaranton.com/IXFR/IN' denied

18-Mar-2011 14:32:18.015 security: error: client 174.37.196.55#50783: zone transfer 'cheshirecat.net/AXFR/IN' denied

Here is the relevant part of named.conf.

options {
        directory "/etc/bind";
        pid-file "/var/run/named/named.pid";
        files 4096;

        allow-transfer { 140.186.190.103; 84.234.24.90; 207.246.95.34;
                         203.20.52.5; 140.186.190.103; 127.0.0.1; 174.37.196.55; };
};

logging {
channel "bind" {
    file "/var/log/bind.log" versions 3;
    print-time yes;
    print-severity yes;
    print-category yes;
    severity info;
};

category lame-servers { null; };
category "default" { "bind"; };
};