When trying to import from Google Drive, the following error is shown:

You don't have the required administrator permissions to migrate from Google Drive in administrator mode.

You need to have the "Super Admin" permission on your Google Apps domain in order to use the administrator mode. This error will also occur if you are trying to use the administrator mode while using your personal account, which usually ends with @gmail.com or if your account is suspended.

To fix this issue follow the Setup part of the administrator mode documentation.