IK is your best bet. If you want to keep the end effector position constant between the start and end, you can do it as follows
Ah, the planning_test.py has a bunch of flags at the top of the file to test more complex version of the motion planning functions, and these were set to 1 in the committed version. They should be set to 0. If you git pull, the most recent planning_tes...
This type of thing happens usually when the PID controller is going unstable, or when the object is already penetrating through the robot upon simulator initialization.
Can you attach the code, robot file, and object file that generates this error?