A message displays in a Layout image frame when the image file that the frame references cannot be found. The message includes the path to the file that is missing. The image frame retains the reference to the image, so restoring the image file restores its display in the image frame.
As an example, you will see a message after deleting or renaming the image or when an image is in a shared location on your network and you lose access to the network. After restoring the image, or restoring your network connection, the image displays in the layout.
The Layout retains the image in the layout during your session, so you may not see a message until after reloading the layout, such as when resizing the image in the layout or after opening a workspace.