What does "Unable to map UPnP port to xx.xx.xx.xx:xx" mean?

This error means that µTorrent was unable to map the port with UPnP. If you have a green status light or have forwarded your port manually, you can safely ignore this error. However, if you have a yellow/red status light, it may mean that you need to forward the port manually, or that your firewall is blocking incoming connections. UPnP will currently only work on Windows XP in 1.5, so other OSes will need to forward manually. However, 1.5.1 beta 462 and later support UPnP on ALL OSes.