Cubase 8.5 elicencer problem

Since upgrade to 8.5 version of Cubase Pro my e-licenser dongle isn’t recognised by my stand-alone studio PC running Cubase 4 and Cubase 8 Pro (no internet connection).

I have 3 PC’s.
a) Studio PC running Cubase 8.0.1 Pro (and Cubase 4) (Windows 7)
b) Older laptop running Cubase 8.0.1 Pro (and Cubase 4) (Windows 7)
c) New laptop running Cubase Pro 8.5 (Windows 8.1)
plus the e-licenser dongle which is showing a licence for Cubase Pro 8.5 on both the laptops that have internet connections.

When I plug the (updated/maintenance) dongle into the studio PC it says the licence for Cubase is not recognised. The same thing happened when I first plugged the dongle into the old laptop, which then performed an on-line maintenance and then recognised the dongle. (I can’t do this with my studio PC and the dongle still remains unrecognised by the studio PC).

Additionally, on the two laptops (that do recognise the dongle) I am getting runtime error messages (visual C+++) and start-up crashes when I try to open projects from earlier versions, so I can’t access my projects that I recorded/mixed in earlier versions (4 & 8). I never had this problem in the past (before 8.5).

Questions for solution:
a) How do I manage to get my studio PC to recognise the dongle? (It recognises the licence for the Blues Essentials pack and recognised the dongle when I upgraded from Cubase 4 to Cubase 8).
b) Is there any reason why 8.5 won’t open Cubase 4 & 8 .cpr files? (I’ve always been able to copy projects between machines in the past via an external hard drive ‘copy’ transfer).
c) Will Cubase 8.0.1 open files saved in Cubase 8.5?
d) Is there something I have forgotten in order to manually activate the e-licencer dongle on the studio PC (no inter-net)

I have all the crash dump files available if needed by tech support.

Additional info: I saved a project in Cubase 8.5 (laptop 2) and then transferred and opened it in Cubase 8.0.1 (Laptop 1) … so Cubase 8 does open the 8.5 projects.

I still can’t understand why my studio PC (running Cubase 8.0.1) won’t recognise the Cubase license in the dongle - (as it recognises the Blues Essentials SE pack and my Korg and Arturia licences) . The only difference between the studio PC and the laptop running Cubase 8.0.1 is that the Studio PC doesn’t have an internet connection.
It was working perfectly until I upgraded Laptop (Laptop 2) to Cubase 8.5 … and the dongle auto maintained to a Cubase 8.5 license …

I’d just like to understand how the dongle licensing recognition works before I strip down and reload the studio PC …