I think you might have a mix-match between some old and new version. If you found a link for the Addon Manager in the forum, it was probably some temporary test version that was uploaded to help someone with issues.
But, the one and only official link for the always current version, it's always on each Product "Info" page, that contains the links for the Stand-Alone Addon Manager, both for FS9 and for FSX.
In any case, KLAS always had a self-updating installer so, it should be able to always get the current version of the Addon Manager, since the installer it's just the same, and takes the files always from the same URL. The only difference, the Stand-Alone installer doesn't have a scenery with it, so it's a smaller download.
Another possible issue might be that, instead of the Addon Manager being the problem, some of your KLAS files changed on your hard drive, for any reason, and this will be reported as being an old version too. This should be fixed by Uninstalling then Reinstalling the scenery.