APM Planner 2.0.15 with OS Xv10.10.1 won't connect to USB Tx

Thank you for the opportunity to post my question to the forum. I have reviewed prior posts and found this problem previously addressed but I did not find a solution to my specific problem.

I have installed the driver for the 3DR radio to connect to a USB 3.0 port on my MacBook Pro and then installed APM Planner 2.0.15. With the 3DR radio on the 3DR X8+ (purchased in December, 2014) correctly installed and the X8+ powered up, the LED on the radio connected to the MacBook Pro changes from blinking green to continuous green. I interpret this to mean that the two radios are connected. Yet when I click on the “connect” link at the upper right corner of APM Planner, the Planner does not connect to the radio link. The display of the various windows of Planner appears normal judging from YouTube tutorials on this topic that I reviewed. I would appreciate advice about how I can get the Planner software to connect to the radio. I looked for a log file to send but I was not able to find one.
Thank you.

Click on the device ID box and then select the radio and set the baud to 57600