Hi,
Curious, what version of VI Client are you trying to use?
Down here I just tried to connect to a WS12 setup using both VI-Client from vSphere 6 (did not work, wanted to download a new installer and then failed) and from another machine use vSphere 5.5 VI-Client (reported "Error:Server did not provide session cookie") also failed.
FWIW I was able to connect from Fusion 7.1.3 without issues and that appears to work OK.
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Wil