I have the same problem. The FSX and FSX-SE registries entries are exactly as you say they should be. Yet still GSX will not install properly.
But you must have the *current* version of the installer!
I'm sure the registry is correctly set up as I am able to install legacy FSX addons with no problem as they see FSX-SE as being FSX.
That's precisely because they ARE legacy so, they only thing they know is the FSX registry key, so they are unaffected by a messed up FSX:SE registry, which is something they don't even know.
Since GSX is a *proper* FSX:SE+FSX product, it must support:
- FSX Stand-alone
- FSX:SE stand-Alone
- FSX + FSX:SE installed together
That's why it requires the registry entries are correct for any given situation, which they usually are, if nobody touches anything.
Unfortunately, it seems that someone out there is suggesting to screw up your FSX:SE registry keys that way in order to let you install FSX-specific product, by simply have the FSX key pointing to it, and this is wrong, because even if it would work with a "legacy" product that only knows about FSX, it will of course confuse the GSX installer, which needs to recognize every different case.
When the FSX key points to FSX:SE, indicating an FSX:SE stand-alone install, the other keys must be changed accordingly: the FSX:SE key shouldn't exists, and the Co-existence key MUST be 0, assuming you really got rid of FSX.
I eventually got GSX working successfully by using the following steps:
1. Deactivate GSX licence from Addon Manager window
2. Uninstall GSX, addon manager, couatl
3. Download latest GSX installer from FSDT website
4. Installed GSX
5. Load FSX and activated GSX licence
6. Exit and restart FSX
None of these steps was required, except #3, the "Download latest GSX installer from FSDT website".
Nothing related to the license every happens while installing. You can uninstall/reinstall an unlimited amount of times, and nothing will happen to the license activation, unless you also upgrade hardware or reinstall Windows from scratch in the process.