Accounts :: Unable To Sign Into Any Newly Created User Account

Updated to 8.1, created a couple of users accounts - but unable to sign into these accounts. Clicking to sign in, simply shows (a few seconds later) - 'Signing out'. No errors or similar reported and nothing obvious in the Event Log of the Admin user.

Have tried a variety of accounts - with passwords, without, child accounts, etc - same result.

Any accounts existing prior to 8.1 seem to work okay.

Safety Scanner and SFC check found no problems. A bit more testing found that if I create a new Administrator user, then this user can be logged onto and works fine. Whereas the Standard or Child accounts still won't logon. Accounts created using a pre-existing 2nd Administrator user (i.e. pre 8.1) show the same behaviour.

Logged on as Admin1 (my account).
Created W-user2 (child user) - unable to logon
Created test-user (std user) - unable to logon
Created test-21-1 (std user - created 21/10/13 after sfc check) - unable to logon
Created Admin3 (admin user) - Logon successful

Logged on as Admin2 (pre-existing 2nd Admin account)
Created standard2 (std user) - unable to logon
Created child2 (child user) - unable to logon
Created Admin4 (admin user) - Logon successful

So, it looks like only new Admin users can logon. A pre-existing Standard user account can still logon (as before).