Thanks for taking the time to post a reply. I don't have an error message nor have I tried any other software as I do not have access to a Mac Book Air. I am simply getting the information from the Garmin Forums from where the previous quote was copied. What I cannot understand is why a Garmin Montana which works OK when linked to a Mac pc with usb2 will not apparently work with a Mac Book Air when using a usb3 which I understand to be backward compatible.
So, re-reading the entire thread, you don't actually know if it will work or not because you haven't bought the MBA, don't have the software and haven't actually attached (or tried to attach) your Montana to a USB3 anything, much less an MBA. You seem to be reacting to something you read somewhere, with us chasing all around finding solutions you can't try.
Here's a practical suggestion: take your Garmin, and the cables for it, to an Apple store or Apple seller, see if you can get them to let you see if the Garmin can attach to the MBA you are interested in, with the understanding that if it does, you'll buy that MBA right there, on the spot. I would bet that they would, under that condition, let you try it, maybe even let you install the software on it from Post #2 (which has, BTW, been updated to run under ElCap, the latest version of the OS).
Alternatively, and somewhat less honorable, IMHO, you can buy the MBA from an Apple store, try it right away and if it doesn't work, take it back for a refund. Last time I checked Apple was taking back systems for 14 days after purchase. Here's the policy they use:
http://www.apple.com/shop/help/returns_refund