Greetings all,
I have just installed ArcGIS for Server 10.4.1 (workgroup) on a clean, new VM (W2012R2), All is working well. A certificate has been installed And all's well. I can publish and consume services without an issue.
I have installed the ArcGIS WebAdaptor 10.4.1 (WA) on the same machine. Called it Obi (after my Habaneese), and using https.
When it comes time to register the WA with Server, I am getting the following error:

Has anyone experienced this issue? I have installed the WA since 10.3.1, and 10.4, a few times, but never had this issue.
I have tried, uninstalling/reinstalling, make sure I have all the necessary IIS requirements, etc. Nothing seems to be amiss.
Thanks in advance for any input.