[firedrake] Problem with nonlinear solver on extruded mesh

[Anna Kalogirou]

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.