If both the Red and Green LEDS on the Comfort PCB remain on after a reset, the whole system will not work.
This means that there is an incompatibility between the Comfort firmware and the File System which has been downloaded to the U4 Nonvolatile Memory. To fix this, download a default file with the correct File System. In Comfiguratior, select File > New. And select the correct template for the firmware. eg Comfort II Ultra. Check that the File System displayed on the lower right corresponds to your Comfort (Ultra II = File System 34, Optimum II = File System 31). Download with Transfer > Download (PC -> Comfort). There may be a warning message that the File System is incompatible with the Comfort version; ignore this an proceed with the download).
After the download, the system wil be reset, and only the Green LED should remain on.
Once the correct file system has been downloaded, do not ignore the warning (File System is incompatible with the Comfort version) as it means that you are about to download the wrong file system, which caused the problem in the first place.