A PADO (PPPoE Active Discovery Offer) is a packet that should be sent back to your computer after it sent a PADI.
In the case of a UTD connected via Ethernet, this is the response that is supposed to come back from the modem, after your IPCOP sent a PADI (to discover PPPoE capable devices).
If no PADO is received after sending a PADI, the message "Timed out waiting for PADO packet" or such, is printed in your system log.
What it means is that the modem didn't reply to a PADI as it should have. This seems to be laregely due to a buggered up firmware update that went out to some of the modems. You could try manually downgrading to a previous version of firmware for the UTD. The other possible is that the ethernet connection between UTD and modem is disconnected, or that the UTD or PC ethernet is buggered.
If I recall there's a couple of files on the iBurst website.