Simple plot command fails

Still no luck. I am not trying to run this

   > interactively. Switching between TkAgg and GTKAgg
   > does not seem to do anything.

Did you try rm -rf your old site-packages/matplotlib and your build
subdirectory of the matplotlib src tree, and rebuild/install
matplotlib cleanly?

If that fails, it might be instructive to edit
"/local/lib/python2.2/site-packages/matplotlib/", line 234,
and print len(x), len(y) and seeing what the hell is going on, since
the last error is

    if midPoint and self.gridOn: self.gridline.draw(renderer)
  File "/local/lib/python2.2/site-packages/matplotlib/", line 234,
in draw
    xt, yt = self._transform.numerix_x_y(x, y)
ValueError: x and y must be equal length sequences

Finally, I can see that this is an error arising from drawing the
grid. Does it go away if you turn the grid off (axes.grid : False in
rc and comment out the grid call in simple_plot).

I'm grasping at straws here - my best guess is above, that you have
some incompatible old matplotlib lying around.