vCenter Server 8
The vCenter that you're trying to log into doesn't have the SSO domain that you're trying to login with, and the account isn't being locked out because it doesn't exist.
1. Determine the correct SSO domain by performing either of the following:
vsphere.local2. Attempt to log in with the correct SSO domain. If this still fails, you can reset the password by referencing vCenter SSO password login fails with error "User account is locked. Please contact your administrator"
3. After you've successfully logged into the vCenter UI, if you'd like to change the auto-generated password from step 1, reference Change Your vCenter Single Sign-On Password