Twinx/Pandas dev error

twinx-pandas.txt

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-1-27f6bdaefe81> in <module>()
     31 
     32 raints.plot(ax=ax3, alpha=0.5, lw=1, color='b')
---> 33 gwets.plot(ax=ax3, kind='line', lw=2)
     34 ax3.set_title('Rain and GWE on one axes')
     35 

c:\Python27\lib\site-packages\pandas\tools\plotting.pyc in plot_frame(frame, x, y, subplots, sharex, sharey, use_index, figsize, grid, legend, rot, ax, style, title, xlim, ylim, logy, xticks, yticks, kind, sort_columns, fontsize, secondary_y, **kwds)
   1284                      sort_columns=sort_columns, secondary_y=secondary_y,
   1285                      **kwds)
-> 1286     plot_obj.generate()
   1287     plot_obj.draw()
   1288     if subplots:

c:\Python27\lib\site-packages\pandas\tools\plotting.pyc in generate(self)
    588         self._compute_plot_data()
    589         self._setup_subplots()
--> 590         self._make_plot()
    591         self._post_plot_logic()
    592         self._adorn_subplots()

c:\Python27\lib\site-packages\pandas\tools\plotting.pyc in _make_plot(self)
    916         # this is slightly deceptive
    917         if self.use_index and self._use_dynamic_x():
--> 918             data = self._maybe_convert_index(self.data)
    919             self._make_ts_plot(data, **self.kwds)
    920         else:

c:\Python27\lib\site-packages\pandas\tools\plotting.pyc in _maybe_convert_index(self, data)
   1043             if isinstance(freq, DateOffset):
   1044                 freq = freq.rule_code
-> 1045             freq = get_base_alias(freq)
   1046             freq = get_period_alias(freq)
   1047 

c:\Python27\lib\site-packages\pandas\tseries\frequencies.pyc in get_base_alias(freqstr)
    445     Returns the base frequency alias, e.g., '5D' -> 'D'
    446     """
--> 447     return _base_and_stride(freqstr)[0]
    448 
    449 _dont_uppercase = ['MS', 'ms']

c:\Python27\lib\site-packages\pandas\tseries\frequencies.pyc in _base_and_stride(freqstr)
    424     _freq_and_stride('5Min') -> 'Min', 5
    425     """
--> 426     groups = opattern.match(freqstr)
    427 
    428     if not groups:

TypeError: expected string or buffer