I figured the issue, what had happened is during or post installation the shortcut to fsxhad lost the tick against 'run as administrator'.
Well, that's something that *has* been done by our installer. But that's for a reason: it's necessary to turn off the "Compatibility" mode, which shouldn't be enabled in FSX, and it causes a lot of problems.
If you *never* ran FSX as a "normal" user before, it's understandable that FSX asked for activation again, since it never recorded the activation in your "normal" user account so it's not that you "lost" it, it was still there, as Administrator, but it was never being recorded as a normal user.
However, you shouldn't run FSX As Administrator, it's not required at all. If some developers told you to do that in order to run their products, it's a cheap way to ignore the real issue, which is their products are wrongly trying to write into the FSX installation folder that, under the UAC rules, can't be written if FSX is installed under C:\Program Files, which is not-writable by default on a Vista/Win7/Win8 system. A product fully compliant with Vista/Win7/8 should only write into the proper locations, like %APPDATA% etc.
Running FSX As Administrator bypass this, but at with an high security risk, since ALL your system is exposed to a potential bug of an FSX add-on module, that can do everything on your system.
A more correct approach, would be changing the permissions for the FSX folder, and grant regular users the permission to write, in that folder *only*, not your entire system, which is what running FSX "As Administrator" does. This will fix all problems with non-compilant addons, whose developers told you "run FSX As Adminstrator"...
