A support displacement load (SDL) can be applied only to points where the nodes are restrained along the direction of the SDL. You do not have any supports at nodes 2 and 3. Add the following to get around this problem.
2 3 ENFORCED BUT FX FZ MX MY MZ
You are stating that "The joints 2 and 3 should simply go down and transfer all forces (400 kN) to Beam 9 and 10". Can you explain why that should happen? Are members 11 and 12 going slack when joints 2 and 3 displace downwards? Is this why you are declaring members 11 and 12 to be INACTIVE?