After not having any trouble with my iMac (10.11) or any mac recognising my android samsung phone today this iMac decided it would no longer cooperate. This morning after waiting a long time and trying different things ( from forums) there was finally a connection but now ( late afternoon) it won't work again. And I got the feeling when the connection was established it was luck and nothing to do with any settings most of which the phone doesn't seem to have as described on forums. As said it has worked automatically on the iMac before and still works immediately on the old mini ( 10.7) Normally I plug it in and it instantly comes up and asks for UMS setting or the other one which I have never used. I intensely disliked the phone when I got it few years ago but it takes good photos and always loaded onto the mac so decided to use it as camera only. I have tried different cables and plugged it directly into computer but doesn't fix the problem.