[away3d] Error: isNaN(sz) ?

[Mech7]

I have some buttons on a plane, and usually it goes good.. only
sometimes when I click them I get this:

Error: isNaN(sz)
        at away3d.cameras.lenses::ZoomFocusLens/project()
        at away3d.core.project::MeshProjector/primitives()
        at away3d.core.traverse::PrimitiveTraverser/apply()
        at away3d.core.base::Object3D/traverse()
        at away3d.containers::ObjectContainer3D/traverse()
        at away3d.containers::ObjectContainer3D/traverse()
        at away3d.containers::View3D/render()
        at ebook::Book/render()

Does anybody know what it means? I only change the zoom with scroll
and the focus never changes on a hovercam.