Again, I had this problem - it's like deja vu
For me, this error was generated by my entry in the eqhost file in the Everquest directory of the machine running the server.
host=localhost:<yourport> worked OK
host=127.0.0.1:<yourport> worked OK
host=<yourIP eg 192.168.0.2>:<yourport> gave me the error you describe.
NB Even when I had this error, I could choose 'ignore' from the error window and still connect from the hosting machine. However, I never managed to get another WAN client connected, and gave up and used a private login (which suits my needs).
Hope this helps, good luck (you're almost there methinks).