Root Password Not Recognized, Even After Change

Hello,

I have a VMware ESXi 6.5 host on which I cannot access the root account. Each time I attempt to login, either via the Web interface or via SSH, it tells me that the password is incorrect.

Fortunately, I do have another user with admin access on the machine, so I can still get in. If I log in as that user, and then reset the root user's password, it appears to work, but I am still unable to login as root. This is true whether I reset it via the Web interface or via the shell with the passwd command.

No matter what I do, it tells me that the password for the root account is incorrect.

Any suggestions?

Thanks.