Hi together

I have 1 BV11 and 2 Avants on the same Network-/Masterlink. There is also a MLGW. In the MLGW I can proper assign the BV11 and also 1 Avant. When I want assign the second Avant, in the MLGW its field is blue highlighted. What is wrong? Can i only assign 1 Avant?

Regards, Hermann