StaticMeshComponent SetMaterial crash

Hi,

I have problem with changing material on every tick.
This causes crash after half minute :

m_pxSelectionBox->GetStaticMeshComponent()->SetMaterial(0, xCell.IsValid() ? m_pxSelectionBoxMaterial : m_pxSelectionBoxInvalidMaterial);

This is the callstack :

Have no idea what is wrong.

Any help ? It’s serious …