Bluetooth speaker error

I'm using a Bose SoundLink bluetooth speaker. I've had it a few months and it worked fine with my iMac when I got it. Now it has connectivity problems. But only with my iMac -- not with my wife's Air or her iPhone, those work fine. (The Bose 'remembers' up to six paired devices.)

My iMac discovers the Bose fine. And then it says it connects (and you can see the green light in the bluetooth preferences), although I don't get the beep from the Bose that should indicate a connection -- but if I try to send music to it, the Bose beeps and gives me an error:

"A Bluetooth audio error occurred. There was an error connecting to your audio device. The encoded audio stream configuration was unacceptable to the remote device."

Proximity isn't the issue. And it obviously works fine with other devices, so it's got to be something about my iMac settings. In the bluetooth settings I can watch the Bose go back and forth between "connected" and "not connected." I have tried everything, read every message thread here that pertains to it. I'm at a loss.

Thanks in advance for thoughts...