Hi Steven,
Unfortunately I have tried this and the result is the same error message for me. 
I went ahead and double-checked both using 8080 / no secure channel and trying 443 / secure channel. The error messages are the same as before, respectively, with "Share a Unique Session" selected.
robrtb12,
The url that tests successfully is the same that I attempt the setup with, "vcenter.domain.com". When I select "Connection Test" while on the radio button "Session per user" and input the same user/pass as my configuration attempts, I get the below upon clicking Ok:
~Brandit
Edit:
As a side note, after re-reading I'm sure you were curious as to the exact complete URL. The settings were the same before I clicked Connection Test so I assume (unfortunately vCO doesn't tell me) that it would be the same as well: "https://vcenter.domain.com:443/sdk".