If you are receiving the error message “Another user already paired the HomeKit enabled bridge”, Philips hue labs has a reset for siri voice control on the bridge. This reset will not affect any of your hue bridge settings except for siri voice control. Follow the link below for the reset.

http://labs.meethue.com/support/siri-homekit

Please make sure you are using a device that is on the same network as your hue bridge.