Thanks for the help, folks. It turns out I needed to disable Windows Defender (Firewall) as plus my Comodo firewall well as all a/v during install. However - *after* install, I found I still needed to turn off the Comodo firewall as well as a few options in my MalwareAntiBytes a/v suite.

I have two comments about this:

1) SECURITY: I work in I.T. - and there's no way people should be expected to disable *both firewall and a/v* to install a product. I've seen systems compromised within seconds of being unprotected. I don't know of any other flight sim add-on (that I own at least) that expects this.

2) When running the sim - and getting CTDs due to improper activation - at no stage does an error box pop up to indicate that something has failed. The sim simply quits. This is not what I call user friendly.

In spite of these two moans, I'm delighted to have my 737, 757 and 777 working again!

Adam.