Hi Mathieu,
The preview token expires once the saved information has been archived or published. The preview token generated is only valid for the information being previewed at that time. So if the user is viewing an old link after the content has changed then they will see this error.
Also the error can occur when the website user forgets to click the 'X' button on the preview module to exit the preview. If they forget to do this the cookies might not be cleared and so their web browser can receive old preview data.
You can read how to troubleshoot previews here:
Thanks.