What can I do if after a failed attemp to update the firmware all LEDs are on?

If the firmware update failed and all 3 LEDs are on solid, the unit is not necessarily broken.

Please reboot the unit (unplug AC adapter and plug in again) and test, if the unit is answering to ping on the last knwn IP.
If that works please use tftp –i [IP address of device] put [firmware file] access (example: C:Temp>tftp –i 172.16.3.45 put wpss399.bin access) to update the firmware once again.

If the unit does not answer ping on the last known IP please reset the unit to factory default:
While the AC adapter is plugged in please keep the reset button pressed for about 20 seconds. The unit should then reboot and all LEDs should turn off for a moment. Once this is done the unit should be available on 169.254.111.111 again via ping.
If that does not work please reboot the unit once (plug out AC adapter and in again).

We would recommend not to use Update IP or the webinterface for the update. If you want to update via webinterface there might be security features in your browser that could prevent that data gets send to an unsecure destination. You might need to add the IP of the SX-600 to a list of trusted sites first.

UpdateIP might get blocked from a local firewall.