Interesting scenario here...
vSphere 5.5 U2 with ESXi 5.5 U2 with vDS 5.1 and VDP 6.1.1 working fine
vSphere 5.5 U2 with ESXi 5.5 U2 with vDS 5.5 neither VDP 6.1.1 or 6.1.2 will connect via web client
Has anyone else reporting issues tried with a vDS 5.1 ?