RuntimeError: _image_module::readpng could not open PNG file

Hi all,

How can I resolve this problem

File
"/usr/lib/python2.4/site-packages/matplotlib/backends/backend_gtk.py",
line 303, in expose_event
    self._render_figure(self._pixmap, w, h)
  File
"/usr/lib/python2.4/site-packages/matplotlib/backends/backend_gtkagg.py",
line 70, in _render_figure
    FigureCanvasAgg.draw(self)
  File
"/usr/lib/python2.4/site-packages/matplotlib/backends/backend_agg.py",
line 383, in draw
    self.figure.draw(renderer)
  File "/usr/lib/python2.4/site-packages/matplotlib/figure.py", line
520, in draw
    for a in self.axes: a.draw(renderer)
  File "/usr/lib/python2.4/site-packages/matplotlib/axes.py", line 1416,
in draw
    self.legend_.draw(renderer)
  File "/usr/lib/python2.4/site-packages/matplotlib/legend.py", line
208, in draw
    self._update_positions(renderer)
  File "/usr/lib/python2.4/site-packages/matplotlib/legend.py", line
530, in _update_positions
    l,b,w,h = get_tbounds(tabove)
  File "/usr/lib/python2.4/site-packages/matplotlib/legend.py", line
523, in get_tbounds
    bbox = text.get_window_extent(renderer)
  File "/usr/lib/python2.4/site-packages/matplotlib/text.py", line 458,
in get_window_extent
    bbox, info = self._get_layout(self._renderer)
  File "/usr/lib/python2.4/site-packages/matplotlib/text.py", line 185,
in _get_layout
    w,h = renderer.get_text_width_height(
  File
"/usr/lib/python2.4/site-packages/matplotlib/backends/backend_agg.py",
line 240, in get_text_width_height
    Z = self.texmanager.get_rgba(s, size, dpi, rgb)
  File "/usr/lib/python2.4/site-packages/matplotlib/texmanager.py", line
309, in get_rgba
    X = readpng(pngfile)
RuntimeError: _image_module::readpng could not open PNG file
/home/nwagner/.matplotlib/tex.cache/7215ee9c7d9dc229d2921a40e899ec5f_80.png
for reading

I am using '0.85.cvs'.

Nils