When a new user logins into a machine and attempt to enable BitLocker, he gets the error, "The specified account does not exist."
When the current user account isn’t recognized by the AD, BitLocker receives a standard error code - ERROR_NO_SUCH_USER, which is converted to the standard error message, "The specified account does not exist."
One reason this error message can be thrown is if the BitLocker wizard failed to back up the recovery password to Active Directory because the account is not fully replicated to all domain controllers, in particular the one the client connected to.
Wait for AD replication to complete for the account and try again.
BitLocker, Account does not exist