Hi Bruce.
Please could you advise what version of ActivManager that you have? Please click on your icon and select Control Panel. This information is listed at the bottom.
How long is the cable between your MacBook Air and the ActivBoard? If the cable is more than 5 meters, please test a smaller length USB cable directly into the ActivBoard and see if this helps. You mentioned this was installed flush to the wall, the USB cable will need to plug in behind the ActivBoard approximately behind where the LED in the top left corner is.
Are all of the ActivBoard's standard 300 series (these do not include the speakers)? If possible, please could you provide the product code of the ActivBoard that isn't working with this MacBook? Also, what version of Mac is installed?
If you wish to contact Promethean directly Bruce, please quote reference number which I have created for yourself which is 00423388.
I look forward to your reply.
Adam
Promethean Technical Support