Unity-Technologies/UnityCsReference · error · InvalidOperationException

Cannot replace the Prefab instance when it has a missing scr

Error message

Cannot replace the Prefab instance when it has a missing script. GameObject '{gameObjectsWithInvalidScript[0].name}' has a missing script. Use InteractionMode.AutomatedAction to force the replace.

What it means

Thrown by ThrowIfInvalidArgumentsForReplacePrefabInstance when mode == InteractionMode.UserAction and FindGameObjectsWithInvalidComponent(prefabInstanceRoot) returns at least one GameObject with a missing script. Unity's Undo system cannot record operations on missing scripts, so a user-initiated replace is blocked. The message names the first offending GameObject and tells you to use InteractionMode.AutomatedAction to bypass the Undo constraint.

Source

Thrown at Editor/Mono/Prefabs/PrefabUtility.cs:2271

            if (EditorUtility.IsPersistent(prefabInstanceRoot))
                throw new ArgumentException("Input instance root is from a Prefab asset, this is not supported. Input instance: " + prefabInstanceRoot.name, nameof(prefabInstanceRoot));

            if (PrefabStageUtility.IsGameObjectThePrefabRootInAnyPrefabStage(prefabInstanceRoot))
                throw new InvalidOperationException("Replacing the root Prefab instance in a Variant is not supported since it will break all overrides for existing instances of this Variant, including their positions and rotations." + prefabInstanceRoot.name);
            if (IsAnyPrefabInstanceRoot(prefabInstanceRoot) && EditorSceneManager.IsPreviewSceneObject(prefabInstanceRoot) && prefabInstanceRoot.transform.parent == null) // EditPrefabContentsScope handling
                throw new InvalidOperationException("Replacing the Variant parent is not supported since it will break all overrides for existing instances of this Variant, including their positions and rotations." + prefabInstanceRoot.name);
            if (prefabInstanceRoot.transform.GetType() != prefabAssetRoot.transform.GetType())
                throw new InvalidOperationException(string.Format("Cannot replace the Prefab instance '{0}' with root transform of type {1} with a Prefab asset with root transform of type {2}. Transform types must match.", prefabInstanceRoot.name, prefabInstanceRoot.transform.GetType().Name, prefabAssetRoot.transform.GetType().Name));

            if (prefabInstanceRoot.hideFlags.HasFlag(HideFlags.DontSaveInEditor) || prefabInstanceRoot.transform.hideFlags.HasFlag(HideFlags.DontSaveInEditor))
                throw new ArgumentException("Input instance root is using the HideFlags.DontSaveInEditor flag which is not supported when replacing: Input instance: " + prefabInstanceRoot.name, nameof(prefabInstanceRoot));

            if (mode == InteractionMode.UserAction)
            {
                // Recording undo does not handle missing scripts
                var gameObjectsWithInvalidScript = FindGameObjectsWithInvalidComponent(prefabInstanceRoot);
                if (gameObjectsWithInvalidScript.Count > 0)
                    throw new InvalidOperationException(string.Format($"Cannot replace the Prefab instance when it has a missing script. GameObject '{gameObjectsWithInvalidScript[0].name}' has a missing script. Use InteractionMode.AutomatedAction to force the replace."));
            }
        }

        public static void ReplacePrefabAssetOfPrefabInstances(GameObject[] prefabInstanceRoots, GameObject prefabAssetRoot, InteractionMode mode)
        {
            ReplacePrefabAssetOfPrefabInstances(prefabInstanceRoots, prefabAssetRoot, new PrefabReplacingSettings(), mode);
        }

        public static void ReplacePrefabAssetOfPrefabInstances(GameObject[] prefabInstanceRoots, GameObject prefabAssetRoot, PrefabReplacingSettings settings, InteractionMode mode)
        {
            if (prefabInstanceRoots == null)
                throw new ArgumentNullException(nameof(prefabInstanceRoots));

            if (prefabInstanceRoots.Length == 0)
                throw new ArgumentException(nameof(prefabInstanceRoots) + " has no objects");

            if (settings == null)
                throw new ArgumentNullException(nameof(settings));

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Remove the missing script components from the Prefab instance before replacing (use GameObjectUtility.RemoveMonoScripts or manually remove in Inspector).
2. Pass InteractionMode.AutomatedAction instead of UserAction if you don't need Undo support.
3. Restore the missing MonoScript / fix compilation errors so the component resolves.

Example fix

// before
PrefabUtility.ReplacePrefabAssetOfPrefabInstance(instance, asset, InteractionMode.UserAction);
// Throws: instance has missing script

// after — use AutomatedAction to bypass Undo limitation
PrefabUtility.ReplacePrefabAssetOfPrefabInstance(instance, asset, InteractionMode.AutomatedAction);

if (mode == InteractionMode.UserAction)
{
    var invalid = PrefabUtility.FindGameObjectsWithInvalidComponent(prefabInstanceRoot);
    if (invalid.Count > 0)
    {
        // Either remove missing scripts or switch to AutomatedAction
        mode = InteractionMode.AutomatedAction;
    }
}
PrefabUtility.ReplacePrefabAssetOfPrefabInstance(prefabInstanceRoot, prefabAssetRoot, mode);

static bool HasNoMissingScripts(GameObject root)
{
    return PrefabUtility.FindGameObjectsWithInvalidComponent(root).Count == 0;
}

When it happens

Trigger: A Prefab instance in the scene has a component whose MonoScript was deleted or never compiled (shows as 'Missing (Mono Script)' in the Inspector). Calling ReplacePrefabAssetOfPrefabInstance with InteractionMode.UserAction on such an instance.

Common situations: After deleting a script that was used by Prefabs but not cleaning up the components. Upgrading a project where an assembly is missing and components became 'missing'. Importing assets from a collaborator who didn't include all scripts.

Related errors

• Cannot convert the GameObject when it has a missing script.
• Cannot replace the Prefab instance with the Prefab Asset '{A
• The Prefab you want to instantiate is null.
• ApplyPrefabAddedGameObjects requires that GameObjects share
• ApplyPrefabAddedGameObjects requires that GameObjects share

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/ab0842f1054d6ac3. Report an issue: GitHub.