[firedrake] Freen-Lagrange tensor

Dear firedrakers, I am trying to use a simple finite strain model based on the use of the Green-Lagrange tensor. Unfortunately, I get a strange error : KeyError: 'Object with key a9198fc8d1d6100862060f0212858a83 not found' Am I missing something? Everything is OK when using the linear strain tensor. The script is attached to this email. Thanks for your help, Nicolas