I get no errors running the following:
from dolfin import *
mesh = UnitSquareMesh(10,10)
X = FiniteElement('CG', mesh.ufl_cell(), 2)
Y = FiniteElement('CG', mesh.ufl_cell(), 2)
Z = X * Y
S = FunctionSpace(mesh, Z)
u_Platte = Function(S)
height = 1.0
width = 1.0
length = 1.0
mesh = BoxMesh(Point(0.0, 0.0, 0.0), Point(length,width,height), 10,10,10)
# Build function space
P2 = VectorElement("Lagrange", mesh.ufl_cell(), 2)
P1 = FiniteElement("Lagrange", mesh.ufl_cell(), 1)
TH = P2 * P1
W = FunctionSpace(mesh, TH)
W0 = W.sub(0).collapse()
bc_function = project(as_vector((0,0,u_Platte[0])),W0, solver_type="mumps")