I have the same problem with sensors: i can not add additional sensors to my 2 existed. Two door sensors are working. Looks like A+ trying to add the sensor but than message pop up: failed. Doors sensors are Z-bee. I have tried to add garage door sensor also which is Zig-Wave and got the same message. this is software problem, not sensors.
Only time I've experienced this issue is when the timeout kicked in because I was slow initiating the pairing or with a weak signal from the sensor.
When I relocated the sensor closer to the Almond+, I was able to pair.
Make sure you have the pairing process initiated on the sensor prior to searching for it with the Almond.
Make sure the sensor is close enough to the Almond device.