Sunday night (well, actually Monday morning), 12am I received a frantic call from one of my tenants. He couldn't get into his room, there seemed to be some problem with his key. I asked him if he tried it before he went out, and he said he didn't. It wasn't locked when he moved in, and when he went out he just locked the door.
Then I realized what happened. I had given him the yard door key instead of the master room key. What a blunder! So there was nothing to do but drive all the way to the Domain and get him the right key. Serves me right for being so sure, and not testing the key first before giving it out. J and I had a 1-hour joyride to and fro, and finally got home around 1.30am. One of the lessons learnt as a landlord!