Fix User Unable to Connect to Non-Domain Joined Computers

Were you qualifying the username you entered with the local machine name? If not, it's likely Windows was assuming you were attempting to login as the administrator account for the domain instead of the local system.

In order to explicitly tell Windows that you want to login with the local administrator account you either need to qualify the username using the computer name like MYCOMPUTER\administrator or you can use the "dot notation" like this .\administrator. The dot is an alias that Windows recognizes as the local computer.

Use automatic unlock with the key assigned to a user/group in Active Directory?

In the Bitlocker FAQ, section What is Bitlocker? How does it work?

• Active Directory Account or Group. A key can be assigned to an Active Directory user, group, or computer account and when those credentials are presented the drive will be unlocked. Using this key protector requires using manage-mde or the Windows PowerShell cmdlets for BitLocker to manually add the ADAccountorGroup key protector. For more information on the cmdlet, see Add-BitLockerKeyProtector. For more information on the command-line syntax, see Manage-bde: protectors.