Cannot Build to Oculus because "Saving Prefab to immutable folder is not allowed"

[SSilvermanAmat]

I am in the process of porting a VR project to Oculus Quest 2 device. I am getting this error thrown whenever I try to build to the quest device.

“Saving Prefab to immutable folder is not allowed: Packages/com.amat.levelup.cameramrtk/Prefab/MixedRealityToolkit.prefab
UnityEngine.GUIUtility: ProcessEvent (int,intptr,bool&)”

This prefab is an instance from a downloaded package, however I have not mutated/changed the prefab in any way, but it is still giving this this error when I go to build the scene to quest device.

I have tried unpacking the prefab in hopes the error will go away and “sometimes” this helps me bypass the error and the build will work, but most the time it doesnt. I have no idea what the exact solution to this issue is. I desire some help here if anyone knows of an alternative solution or different perspective to tackle this.

Another Note: I am using MRTK2 within OpenXR framework. Unity version 2020.3.45f

[soleron]

An “immutable folder” is usually a package folder that should not be irrevocably modified, and the system actively prevents that.

I get this error when I have used some prefab from a package folder and try to apply changes to it that would be published with the game. That should not happen.

Perhaps you have already, but if not, make sure you are not using some settings, or a prefab that is part of a package in the package folders. Clone that asset (or the configuration settings or mesh etc) into your project folders, and use that one. There should be no links (mesh, script, configuration file etc.) to the package folders.

Chances are, the reason why sometimes it works when you unpack the prefab and sometimes it doesn’t, is because in some cases, despite unpacking the prefab, something is still being pulled from the package folder.