Thanks to those of you who commended on this one. You were correct in terms of it being a windows 10 issue. Apparently TLS 1.2 certificates are mandated by Windows 10. This issue was resolved by upgrading the ArubaOS on the IAP. The updated ArubaOS includes a compliant TLS 1.2 certificate and as such this is resolved.
Please note, the IAP software was updated by downloading from the Aruba support site as the opton to "check for updates" via the IAP web interface did not access the recently released version. Thanks again for your help, much appreciated. And my apologies for the delayed feedback.