Windows 2008 AD Trust and authentication firewall.

Error on file share opening:
Logon Failure: The machine you are logging onto is protected by an authentication firewall. The specified account is not allowed to authenticate to the machine

The AD external trust setup between DomainA and DomainB is created. External Trust is setup as Selective Authentication, so we need to explicity allow Domain A users access to Domain B Computers.

To allow access open AD Users and Computers –> enable  Advanced Features –> Select the Computer Object –> Properties –> Security –> Add the User or Group You want to allow access to the computer and allow “Allowed to Authenticate”.