Edit: Not sure if my dead script was even the original cause. Submitted a bug report. Details here. Hello, I just ran into this error. Here's a screenshot: After a lot of confusion I eventually figured out what was causing it - I had deleted one of my authoring components that was currently on some of my prefabs that were referenced in the scene. So first off - it would be really great if we could get a more helpful error message for this. Clicking build and seeing the error message "Failed to build entity scene" as my only hint basically makes me want to uninstall Unity forever. Anyways, aside from that I also ran into an issue with trying to get my builds to recognize that I had fixed the problem. I still have a pretty loose understanding about how conversion data gets cached so I'm only going to explain what occured and how I fixed it, whether it's a bug or this is how it's supposed to work, I have no idea. I want to be very clear that I made NO ACTUAL CHANGES to my project between these steps aside from the mentioned attribute changes. Step1 : Replace the dead scripts with new authoring scripts and save the prefabs. Step2 : Attempt dotnet build - same error. Step3 : Add a "ConverterVersion" attribute to my new authoring script that I just added, with a version of "1". Step4 : Attempt dotnet build - same error. Step5 : Increment the converter version to "2". Step6 : Attempt dotnet build - success! Step7 : Attempt wasm build - same error <- This doesn't seem right to me? Surely incrementing the version should have fixed it for both builds? Step8 : Increment the converter version AGAIN (even though I didn't actually make any changes) to "3". Step9 : Attempt wasm build - success! So yeah. Hopefully we can get a better error message for this case, or at least this might save someone from some pointless debugging.