Ok, found the problem, and I think how LM handled the hotfixes is a bit confusing: they have the download link on their forum that indicates the version to be 2.1.10017.0, but the link is being updated with newer versions without changing the link so, you don't know what you'll end up downloading util you download it.
The first hotfix didn't changed the build number compared to the original 2.1 release ( 9936, even if it WAS labeled as "2.1.10017.0" on the link ), but they released further hotfixes without updating the link description, so the current one is 2.1.10210.0, but still labeled as "2.1.10017.0", so we had no way to knowing they updated it without trying...
The issue is, we need to check the build number *exactly* in the installer, because if we jet let you install into any 2.1.x version, the Addon Manager would crash the sim, since it needs to be updated for each build in order to get some informations directly from memory. Just like FSUIPC, basically, every new build of the sim requires a an updated build of the module.
There's an updated Stand-Alone Addon Manager now that recognizes the new build, but you'll have to wait a couple of hours for all the other products installers to be updated too.
