Explanation: A new synthetic image cannot be formed because of a problem with the required component images. For example: a new, synthetic full backup is tried from the previous full image from Sunday and from the five differential incremental images from Monday through Friday. This error occurs if any of those images (except the most recent image on Friday) has expired.
Recommended Action: Run a non-synthetic backup (either a new full or new cumulative), depending on the type of backup that failed.