Hello Wayne,
Sorry to intrude on this conversation but it’s the only question that I’ve found which is similar to my problem…
Like kjcummings, I opened a file of my Rivet Animation but the Character was missing in the scene (see on the picture)

A potential solution that I found was to go in : File – External Data – Report/Find Missing Files
Save the scene and open it again… I tried but I think I broke the Rig…
When I do this technique, I can see my character again but the mesh doesn’t follow the rig anymore and make weird stuffs…

Do you have a solution ? Pleeeeeeaaaaaaase…
Thanks in advance and sorry for my english…