I have looked closely at the questions on this topic and the replies and have tried all the solutions suggested. I have followed this (excellent) video tutorial to the letter:
https://www.youtube.com/watch?v=2O_8HAsz_gU
(ie I created my certificate, my AppID, and my Provisioning Profile).
But still I get this error message: "The Developer Disk image could not be mounted. (Your) iPad may be running a version of iOS that is not supported by this version of Xcode".
I am running OSX 10.10.5 on my MacbookAir, am running iOS 8.4.1 on the iPad that I have plugged into the MacbookAir (and on which I am trying to run the demo App) and am using Xcode 6.3.2.
If anyone has any suggestions, I would be so grateful.
Thanks!