Try these solutions:
1. Make sure that a connected computer can access the Internet (i.e., can browse the web) using the same network.
2. Make sure that a DHCP server is available, or that you have configured a static IP address on the 851N.
You can configure a static IP address on the 851N using the menu item Settings > Network Config > Edit Config, and then select ‘No’ for ‘Auto (DHCP)’. DHCP is however the recommended method.
3. Make sure that the UPnP is enabled on your router if this is an option.
4. Check that your network’s firewall is not blocking any outgoing ports.
As a minimum, the radio needs access to UDP and TCP ports 80, 554, 1755, 5000, 6000 and 7070.
5. Check your access point does not restrict connections to a particular MAC address
You can view the radio’s MAC address using the menu item Settings > Network Config > View Config > MAC address.
6. If you have an encrypted Wi-Fi network, check that you have entered the correct key or passphrase into the 851N.
Remember that text-format keys are case sensitive. If, when attempting to connect to an encrypted network, your 851N displays: ‘Wireless error’ followed by a 5-digit number, then please ensure that you enter the correct passphrase for the network. If the problem persists, then you may need to consult your network configuration.
7. Check the Wi-Fi dongle is securely connected to the unit, and in the correct USB port labelled ‘Wi-Fi Dongle’.
8. Check the units Wi-Fi signal strength.
You can do this by pressing and holding the front panel 'i' button.
If signal is low, try connecting your 851N directly to your router using a wired Ethernet connection.
9. Reboot and/or factory reset your router.