You could get that error if the UDP port specified for the mailserver and chatserver in eqemu_config.xml is in use by another program:
Code:
<chatserver>
<host>192.168.1.x</host>
<port>7778</port>
</chatserver>
<!-- Mailserver (in-game mail) information. DO NOT EDIT -->
<mailserver>
<host>192.168.1.x</host>
<port>7778</port>
</mailserver>
Try changing the number in red to another random port number (they need to be the same port number though, for legacy reasons).
The 'DOS' command, netstat -ano will tell you which ports are already being used by programs on your computer.