This error message means: USB device is already opened.
You could try to set another device as default sound/midi interface in your audio midi settings panel, and also make sure there’s no another (eg DAW) using the uTrack24 when you try to update the devie.
Thanks for the help. I tried as you had suggested, and I even removed all usb connections and hubs to my MAC except for the Utrack connection, yet it still gave me the same error.
I ended up just updating it via the network method.
Anyway, just figured I’d reply for the benefit of others.