Dear all, I am experiencing a problem with extruded meshes. When I try to solve the nonlinear VP: m = IntervalMesh(N,L) mesh = ExtrudedMesh(m, layers=10) F = ( v*(p1-p0)/dt + v*(h0-1) + sigma*inner(grad(v),grad(h0)) + 0.5*inner(grad(p0_5),grad(p0_5))*v )*dx + E_t*v*ds_v(1) I get the error File "/opt/firedrake/2.0/lib/python2.7/site-packages/firedrake/variational_solver.py", line 97, in __init__ form_compiler_parameters=self._problem.form_compiler_parameters) File "/opt/firedrake/2.0/lib/python2.7/site-packages/firedrake/assemble.py", line 58, in assemble form_compiler_parameters=form_compiler_parameters) File "/opt/firedrake/2.0/lib/python2.7/site-packages/firedrake/assemble.py", line 79, in _assemble kernels = ffc_interface.compile_form(f, "form", parameters=form_compiler_parameters) File "/opt/firedrake/2.0/lib/python2.7/site-packages/firedrake/ffc_interface.py", line 273, in compile_form ((kernel, needs_orientations), ) = ffc_kernel.kernels ValueError: need more than 0 values to unpack However, this problem does not arise when I switch to a RectangleMesh ( and change the ds_v(1) to ds(1) ), OR when I solve the corresponding linear VP. Anyone has any ideas why this is happening? Thank you. Best, Anna.