Can not plot second time

import wx

    > from pylab import *

You should not import pylab if you are embedding matplotlib in a GUI.
pylab controls the GUI as a convenience for writing quick scripts, and
so if you want to control the GUI you cannot use it.

See the examples/embedding_in_wx*.py and
http://matplotlib.sourceforge.net/faq.html#OO

Hope this helps,
JDH