I just had this, and wanted to post the answer so the next poor sole doesn’t spent an hour and a half having kittens because they can’t login
A small system 5 users, running in a virtual machine, nowhere near the limits of the virtual hardware. As Admin, and husband to one of the other users, I know both the admin and her passwords.
I couldn’t login as my ID, I could as My wife, and as Admin. Changed the password from both the login screen and the syetem reset password option. Didn’t work
Ran a repair, tried both options again, Didn’t work.
Bear in mind I’m a VMware trainer with 22 years in the industry, tried rebooting, looked on forums, nothing.Getting worried.
Then wife, who is an accountant, suggested changing the account / username, WORKS!!
No idea why, but it does, now I have humble pie as my wife “is smarter” than me, well I knew that anyway.
So I hope this helps