There seems to be an issue lately with some modems and long uploads. My SB5120 logs stuff like: 2009-10-23 12:05:37 5-Warning TSM: TxError WatchDog - Restart Upstream 2009-10-23 12:05:37 5-Warning HAL: Overcoming Tx Error (reseting the US - DMA)
Other modems may be having similar issues, but don't log it. Too many errors over a certain time period, and it may decide to reboot.