The server is not operational - users from a second domain

Hi,

we use MS SAP BPC 7.5 SP3 installed in Domain AAA, our server is called "DEV"

In Server Manager, "Define System User Groups", the domain type AAA is correctly configured as Active Directory and it works fine: I can add users from this domain.

We have to add users from a second domain. In "Define System User Groups", I add the new Domain, called BBB.it, as Active Directory.

Domain AAA and Domain BBB are fully trusted. The server "DEV" use DNS IP of Domain AAA and DNS Ip of Domain BBB.

When I go to the BPC Administration, User, Add new User, I click in the new Item List of the available domains, "Domain BBB", but I receive the message: "The server is not operational [BBB.it]".

How I can solve this problem?

There are specific configuration steps that I missed?

Thank you in advance,

Marco Minaudo