Just installed win10 (build 10130) last night onto my Asus laptop. I upgraded from Win 7 Home.
There was only 1 user on Win7, me, system admin. On the first upgrade, after attaching my profile to my Windows account, after the first reboot, I could no longer successfully fully log in to my desktop on my account. I got the "Critical Error has occurred in the Shell Infrastructure Host ....." message.

So I rolled back to 7, made another admin account ("Sam Samson"), just in case, and re-updated.

I re-attached my main account to my Windows account. Got the same critical error. Sam (and another new account, Mitch), seem to work fine. However, on the login screen, there are now 2 "key" icons named "password". They seem to belong to the Sam and Mitch accounts, but I can't find ANYTHING on the internet about this.

So 2 questions:
1. What are those keys, and
2. Can I recover my user? I've tried sfc and many, many reboots. Even tried startup recovery.

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