Had this problem.
I think it was a bad material (I deleted a .png that was sampled as a texture in that Material)
That material was used on a model in a BP, and that BP was mentioned in the error.
I fixed the material (which I think fixed the problem).
But as a standard practice I also flushed out all the junk in my project folder (which tends to fix a lot of bugs in general, it’s like step 1 when I get errors)…
To do this you keep your project file, Config Folder, Content Folder, Saved, and Intermediate Folders… and DELETE all the other folders in there (except plugins if you’re using any installed there, that probably means keeping a plugins folder if it’s there).
You also get rid of EVERYTHING in the Saved and Intermediate folders EXCEPT for the Config folder in each of them.
That leaves you with the bare bones of your project (everything that Unreal doesn’t generate on compilation). As I understand it, doing this gets rid of builds, binaries, caches, stuff like that.
I understand people feeling scared when you do this process for the first time, it feels like deleting a bunch of stuff. It is deleting a bunch of stuff (can save you a whole lot of storage space)… so feel free to duplicate the project folder, (renaming the folder, and your project file, so they’ll appear under those names when you open Unreal and browse your projects)…
This sort of spring cleaning can really fix some stuff and has helped me in the past.