I always leave the headlights in auto on my 2000 XKR coupe and never had problem until now. One night recently the headlights would not come on regardless if in auto or on. I had no choice but to drive and since the fog lights are so bright I went for it. After about 10 minutes the lights came on. This process has repeated many times. Right now the lights are staying on during the day in auto.

 

My first thought was the sensor, but given your erratic results, maybe the switch stalk? Check the wiring to make sure nothing is loose or frayed.