Windows skel has an issue with this, so if there is an issue, use default path to cache file.

gui/graphFrame.py

@@ -42,7 +42,12 @@ class GraphFrame(wx.Frame):
 
         try:
             import matplotlib as mpl
-            cache_dir = mpl._get_cachedir()
+
+            try:
+                cache_dir = mpl._get_cachedir()
+            except:
+                cache_dir = unicode(os.path.expanduser(os.path.join("~", ".matplotlib")))
+
             cache_file = os.path.join(cache_dir, 'fontList.cache')
             if os.access(cache_dir, os.W_OK | os.X_OK) and os.path.isfile(cache_file):
                 # remove matplotlib font cache, see #234