ImportError: No module named velocity_vector

Dear all,

The problem was as follows.

jiadun@jiadun-Lenovo-IdeaPad-Z500:~/escript-test/examples/usersguide$ run-escript heatedblock.py
Solver: l2/lmax-norm of right hand side is 6.389217e-08/2.246835e-08.
Solver: l2/lmax-stopping criterion is 6.389217e-16/2.246835e-16.
Solver: Iterative method is PCG.
Preconditioner: Jacobi(1) preconditioner is used.
Solver: Step 1: l2/lmax-norm of residual is 1.107460e-07/3.286101e-08 (new tolerance = 7.572139e-17).
Solver: Step 176: l2/lmax-norm of residual is 6.601709e-17/4.341105e-18 convergence!
jiadun@jiadun-Lenovo-IdeaPad-Z500:~/escript-test/examples/usersguide$ mayavi2 -d deform.vtu -f CellToPointData -m VelocityVector -m SurfaceMap
ERROR|2014-07-07 16:29:29,724|No module named velocity_vector
Traceback (most recent call last):
  File "/usr/bin/mayavi2", line 300, in process_cmd_line
    mod = __import__(modname, globals(), locals(), [classname])
ImportError: No module named velocity_vector

Best regards,
Jiadun