Most routers offer a universal plug and play, or UPnP, setting that allows a program to request and forward a port on the router to a specific computer on the network. Not all UPnP requests succeed, however, and when a UPnP request fails to open and forward a router port, the requesting program usually fails. To troubleshoot the error, review the reasons why a UPnP request fails.
UPnP is a setup option for most routers but it's not always enabled by default. If you accept the default setup options for your router and UPnP is not enabled, UPnP requests will fail. Check your router's setup options and make sure that UPnP is enabled on the router if a UPnP request fails.
Port Already Forwarded
When a program requests a port through UPnP and the port is manually forwarded, the request will fail. For example, if you manually forward port 5555 to 192.168.100.1 and a program makes a UPnP request to forward port 5555 to 192.168.100.2, the request will fail because the port is already forwarded. In many cases, the UPnP request will fail even when it's identical to the manual settings for the port. Edit the router's setup options and remove the manually forwarded port for UPnP requests to function properly.
Port Already in Use
Only one computer can use a port at a time. If you have multiple computers on a network behind a single router and a computer makes a UPnP request for port 5555, no other computer can make a successful UPnP request for port 5555 until the computer releases the port. If a UPnP request fails, check to make sure multiple computers are not making requests for the same port at the same time.
Two Routers on the Network
If a UPnP request succeeds but the port is still not forwarded, you may unknowingly have two routers on your network. Some DSL or cable modems have a built-in router. When you add a second router, such as a wireless router, you have to forward ports on the modem to the router because UPnP can only request ports from the closest device. Edit the setup options for either the modem or router and turn off the routing capability by changing the settings from "router" to "bridge."