The value was nothing like the one you gave me, which I changed.
That's the issue, for sure. If it's not 0x23c00 hex ( 146432 in decimal ), Windows will stop asking to trust ANY new executable that has been installed.
Please, double check the value is correct. Do you have any idea what software might have changed that ? Something related to security, perhaps ?
Still no Add on Manager
Have you rebooted Windows ? Have you tried reinstalling only the stand-alone Addon Manager after rebooting Windows following the fix to the registry ?
Come to think of it, I'm nowhere asked for my serial number.
That's obvious: if the Addon Manager is not executing, how it's supposed to ask the serial number ?
The whole issue is to seeing the Windows request to trust the Addon Manager. This request is done by WINDOWS ITSELF. At this stage, the Addon Manager is still NOT running (it would be silly asking the permission to run a software that has already started...) so, everything that happens or not happens at this stage, it's a Windows config error, doesn't have anything to do with our software, that still hasn't got the chance to run, yet.
So, you HAVE to see the Windows request to trust it, if this doesn't come up, than it's sure something is wrong with Windows.
BTW, it might be worthwhile to check if the Addon Manager has been added to your DLL.XML file, which is located at
%APPDATA%\Microsoft\FSX
Check if you see its line in the module's list. Check that it hasn't been disabled ( <disabled>True</disabled ) and verify that the *whole* DLL.XML file hasn't been disabled as well (there's a general switch on top of the file)