Vista Tutorial - DontDisplayLastUserName Problem

Help!

I wanted to have one Vista logon on a computer in which you have to enter the USERNAME and PASSWORD. I found a MANUAL REGISTRY method where you set the "DontDisplayLastUserName" entry to a 1. It worked GREAT on 2 machines BUT the third has a problem. When I rebooted the machine it comes up with ONE logon BUT it will not let me in - "Invalid username or password". Obviously, the username and passwords are correct. Has anyone come accross this situation? Any suggestions would be appreciated. Booting into SAFE MODE - same problem. I would prefer not to have to rebuild the machine. Vista 32 bit Home Premium.

Thanks:

I am Replying to myself here so that it may help someone.

I had to rebuild my machine BUT it allowed me to experiment and this is what I found.
If you have the Guest account disabled then the computer is inaccessible. BUT if the Guest account is enabled (I set it up with no password) YOU WILL be able to sign on using the Guest signon.
If you then try to go to the USER ACCOUNT section, access an account it will prompt you to sign on with an administrator signon. Do so, using the correct password (all passwords and signons are intact). You will get in. If you RESTART your computer or logoff and try to signon as admin you should be successful going forward. ALternatively, you could set up new accounts and delete old ones.
Hope that helps someone. (Remember: Enable the Guest account before applying the the registry "DontDisplayLastUserName" change).
I realise that there maybe other solutions but this worked for me. If anyone has a better solution please share it with us all.

I also have enabled "don't display last user name" in Local Group Policy and also disabled Guest account and I don't have any problem with login to any accont