It's not an error, is a non blocking warning. Anyway, you need to see if the printer is compatible... 

I have experience just with USB thermal printers under linux, I don't know if you can do the same with Lan printers.

open a terminal and fire the command 

lsusb

to get the correct id of the printer and write it to the config file

odoo/addons/hw_escpos/escpos/supported_devices.py

Like this:

 { 'vendor' : 0x0416, 'product' : 0x5011, 'name' : 'Generic USB' }, 

The restart your server and cross your fingers: Odoo has a very poor compatibility with not Epson printers.