The error occurs when attempting to login to any ARCGIS Pro portal.
you may want to have a look at this thread. Maybe it helps.
found this also:
Thanks much. I did see this thread and set the trusted sites as suggested…still no luck. Also I have a support ticket out on this and no luck, even after an hour of screen sharing support.
What version of ArcGIS Pro are you using? ArcGIS Pro 1.3 had a bug which was resolved by installing a patch.
Bug: ArcGIS Pro 1.3 crashes on startup if KB2533623 is not installed on Windows 7 SP1
Thanks, I am using the most recent download as of yesterday. The program does not crash, it just won’t let me log on to any portal. I suspect this may be an organizational security setting and have sent a help ticket to IT security to analyze.
Also Check your computer's ability to run ArcGIS Pro 2.0. Does it pass the recommended requirement?
Can you run Fiddler while you start Pro, then attempt to login? Is your Portal set to http or https? If https, has the certificate expired? Does your workstation trust the certificate on the Portal? Can you authenticate against AGOL? Can you make a "connection" to any Portal (there is no such thing as ArcGIS Pro Portal) in ArcMap? Can you login to the Portal via the Web UI?
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