Make sure your empeg IP address and netmask are compatible with those on your LAN. You can determine the current IP address of the player through the About menu. You will need to either change the settings on your computer to match the player (temporarily), or connect via serial cable or USB to reset the player's ip configuration if they are not compatible.

There is an excellent FAQ that you should read in its entirety. Start with the "Networking and home connection questions" section.

Jim