"get families version error" I perhaps found where does this come from

Probably sometimes when you have tried to download filters fr om the online FF library you have a error message like this "get families versions error", and I did not know what this means and why happens this, and where does it come from.

Well, I have just seen how the Library structure is built and found something interesting that could explain where this error comes from.

Below you can see a screenshot of the "Library Structure" file of FF and there the filters are organized with family ID´s and versions, and everytime you want to download, FF server must get this list and see what filters you already have and what version do you have, and if there is something wrong in this, it can give this misterious error.

But this error gets fixed by itself, sometime after, so I still do know why this happens, but at least I know now wh ere does it possibly come from.