Comment 7 for bug 230973

My UPnP works like charm, but I have no reasons to actually use it.

QQ - Firewall software on the PC (should you be running that) can trigger such "unfortunate events". For some reason, the Windows XP SP2 firewall did the same for me back on my old computer. Something I installed (not sure what) caused it to start blocking applications, seemingly at random. Some would be blocked, most wouldn't.

Also, ESET Smart Security in automatic mode is a killer on DC software.

If you can isolate your computer and the router for the rest of the network for a few minutes, please disable all security systems on your PC and try again.