Ekiga: Error while starting listener for SIP

[^rooker]

[PROBLEM]
When starting Ekiga on Ubuntu 6.06, I received the following 2 error messages (although it did work flawlessly before):

Error while starting the listener for the SIP protocol

You will not be able to recieve incoming SIP calls. Please check that no other program is already running on the port used by Ekiga.

And same for H.323:

Error while starting the listener for the H.323 protocol
...

Since I've just rebooted the computer, I was sure that NO other application was indeed using the same port - so?

[SOLUTION]
My network interface didn't have any IP yet (network cable unplugged) - so there was no interface to bind to - thus, Ekiga was not able to get the port it wanted.