iPython stops plotting

While attempting to debug a bit of numpy code, I am %running a file a few times. Somewhere after several iterations of this (in the 10s--not too many!), the matplotlib plot commands (imshow, quiver) stop working, instead printing the following error. Note that I'm only up to command 54.

This problem occurs using IPython 0.8.2.svn.r2445 on a MacBook running OS X 10.4.

In [54]: plot(vort[127])
---------------------------------------------------------------------------
IOError Traceback (most recent call last)

/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/site-packages/IPython/iplib.py in raw_input(self, prompt, continue_prompt)
   2030
   2031
-> 2032
   2033
   2034

/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/site-packages/IPython/history.py in add(self, ent)
    191
    192
--> 193
    194
    195

/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/site-packages/IPython/history.py in inc_idx(self)
    184
    185
--> 186
    187
    188

/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/site-packages/IPython/Extensions/pickleshare.py in __setitem__(self, key, value)
     84
     85
---> 86
     87
     88

/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/site-packages/IPython/Extensions/path.py in open(self, mode)
    518
    519
--> 520
    521
    522

IOError: [Errno 24] Too many open files: path('/Users/joishi/.ipython/db/shadowhist_idx')