You must be an administrator of this AD LDS instance to import LDIF files. In the unattended setup file, in the SourceUsername ...

You must be an administrator of this AD LDS instance to import LDIF files. In the unattended setup file, in the SourceUsername and SourcePassword fields, type the credentials of an account with administrative permissions for AD LDS.  After you have updated the unattended setup file, run Setup again.