Do you want to create an additional transform for a Windows Installer package (.msi) with an existing transform (.mst), or have you done this and are having difficulty at installation? Are you getting messages in Tuner while working with the transform, or are the messages you are getting occurring at installation?
If you have a Windows Installer package and an existing transform, and want to create an additional transform in Tuner, go to the Create Transform view. Specify the Base Windows Installer Package (.msi). Then list any existing transform(s) in the Provide a List of Additional Transforms field. Then specify the new transform path/name under Windows Installer Transforms and click "Create Blank Transform". The new transform will display your base .msi with and existing transforms applied. Any changes you make will not affect your base .msi or any existing transforms you listed. Changes you make/save will go in the new transform.