I have FA installed in the following directory:
C:\Games\SupCom\Supreme Commander - Forged Alliance\bin\ForgedAlliance.exe
Running FAinstaller.exe opens up the folder C:\Games\SupCom\Supreme Commander - Forged Alliance\bin
I go up a folder and select and it says i do not have the correct version installed.
My version is definitely 1.5.3599 as it says so in FA and has been confirmed with a successfully joined game with FunkOff in GPGnet. Checked that there are no other duplicates installed. And installing the official update says that 3596 cannot be found.
Error: FA is verison is NOT 3599. You need 3599 for FAF. you can download here. Re-launch when it's done.
Install is a couple of years old, will try a fresh install when I wipe the dust off my cd.