Overview:
Unable to upload media file to existing key message, update link is missing, and all configuration is correct.
Root Cause:
VisualForce (VF) page Media File is either not completely registered on the Page Layout or browser Privacy Settings are preventing the page from loading. The Page Layout may appear like the VF page is there when a Media File Name field is placed on the page layout in addition to the VF page which brings in a field with the same name.
Solution:
- Navigate to the Key Message Page Layout be sure the Media File VF page is on the layout.
- Re-Save the page layout.
- If that does not resolve the issue, change the browser Privacy Settings to allow Third Party cookies from the Salesforce (SFDC) org domain (ex: cs22.visual.force.com).
- If the browser used is Internet Explorer, add the domain to the Trusted Sites area in Security Options.
Related Documentation:
SFDC Stack Exchange: Embedded VF Page Not Rendering on Page Layout
Thank you