alphagroup on melco?

[jacobacci]

I have a full license for MinimServer with three installations. Two on Synology NAS and one on a Melco N1A EX.
On the NAS I use alphaGrouping with the following parameters:
AlbumArtist=20, Artist=20, Album=20, Composer=20, Conductor=20, Orchestra=20
I have now tried to enter the same parameters via the Melco instance of MinimWatch. The parameters are accepted when I click apply but when I restart MinimServer it throws the following error:
MinimServer: incorrect name 'AlbumArtist' in property 'alphaGroup'
Am I missing something here?
Thanks for any hints