Exception using PlanToEndEffectorPose in VectorFieldPlanner

[stepelle]

I run

rosrun herbpy console.py --sim

Then, I execute the following code:

robot.right_arm.SetActive()
manip = robot.GetActiveManipulator()
target_ee_pose = manip.GetEndEffectorTransform()
target_ee_pose[2,3] -= 0.2   
planner = VectorFieldPlanner()
traj = planner.PlanToEndEffectorPose(robot, target_ee_pose)

It returns the following exception:

/home/spelle/ros_ws/src/prpy/src/prpy/planning/vectorfield.pyc in FollowVectorField(self, robot, fn_vectorfield, fn_terminate, integration_timelimit, timelimit, dt_multiplier, **kw_args)
    371 
    372         if t_cache is None:
--> 373             raise exception or PlanningError('An unknown error has occurred.')
    374         elif exception:
    375             logger.warning('Terminated early: %s', str(exception))

target_ee_pose is reachable and not in collision.
Any suggestions?