# Accessibility - Instanced Mesh causes exception

**URL:** <https://forum.babylonjs.com/t/accessibility-instanced-mesh-causes-exception/42879>\
**Category:** Bugs\
**Created:** [August 1, 2023, 3:09am UTC](https://forum.babylonjs.com/t/accessibility-instanced-mesh-causes-exception/42879 "2023-08-01T03:09:35Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![NightSkies](https://avatars.discourse-cdn.com/v4/letter/n/71e660/32.png) [@NightSkies](https://forum.babylonjs.com/u/NightSkies)\
**Post date:** [August 1, 2023, 3:09am UTC](https://forum.babylonjs.com/t/accessibility-instanced-mesh-causes-exception/42879/1 "2023-08-01T03:09:35Z")

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Hi,

If you call `BABYLON.Accessibility.HTMLTwinRenderer.Render` then add an instanced mesh using Mesh.clone, an exception occurs while trying to look for the source mesh.  
Kinda confusing because how would there be no source mesh when I used Mesh.clone?

Playground reproduction:

> **[Babylon.js Playground](https://playground.babylonjs.com/#QY6CZS%234)**
>
> Babylon.js playground is a live editor for Babylon.js WebGL 3D scenes

Thanks!

Night

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**Author:** ![Evgeni\_Popov](https://sea2.discourse-cdn.com/flex024/user_avatar/forum.babylonjs.com/evgeni_popov/32/4432_2.png) [@Evgeni\_Popov](https://forum.babylonjs.com/u/Evgeni_Popov)\
**Post date:** [August 1, 2023, 7:52am UTC](https://forum.babylonjs.com/t/accessibility-instanced-mesh-causes-exception/42879/2 "2023-08-01T07:52:32Z")

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Welcome aboard!

cc @carolhmj.

The problem is that the `onNewMeshAddedObservable` observable is notified in the `AbstractMesh` constructor, so the `InstancedMesh` constructor has not been run yet, and the `sourceMesh` property is still `undefined` at that time.

I tried a fix:

> <https://github.com/BabylonJS/Babylon.js/pull/14105>
>
> See https://forum.babylonjs.com/t/accessibility-instanced-mesh-causes-exception/…42879

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<div class="post-metadata">

**Author:** ![NightSkies](https://avatars.discourse-cdn.com/v4/letter/n/71e660/32.png) [@NightSkies](https://forum.babylonjs.com/u/NightSkies)\
**Post date:** [August 1, 2023, 7:56pm UTC](https://forum.babylonjs.com/t/accessibility-instanced-mesh-causes-exception/42879/3 "2023-08-01T19:56:56Z")

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Thanks for the fix! Happily waiting for the patch!