error with basemap and pdf

I have attached a PDF created with matplotib/basemap. On my mac, Preview opens this file without any errors. However, Adobe Acrobat 9.2.0 (Mac) reports this error:

"An error exists on this page. Acrobat may not display the page correctly. Please contact the person who created the PDF document to correct the problem."

It then goes ahead and displays the image correctly.

I have found similar issues with Illustrator, and older versions of Acrobat Professional where those pieces of software are unable to open the PDF at all.

The only free software I could find to validate PDFs (http://multivalent.sourceforge.net/index.html) has no complaints about this file.

Does anyone have any idea what might be causing these errors to (sometimes) occur?

Info:
matplotlib: 0.99.0
basemap: 0.99.4

The code that created the PDF is below:
#!/usr/bin/env python

import matplotlib
matplotlib.use('agg')
from mpl_toolkits.basemap import Basemap
from pylab import savefig,close,figure,arange,array

figwidth=6
figheight=6
clat = 39.132332
clon = -98.261719
fig = figure(figsize=(figwidth,figheight),edgecolor='g',facecolor='g')
ax1 = fig.add_axes([0,0,1.0,1.0])

map = Basemap(resolution='c',
               projection='ortho',
               lon_0=clon,lat_0=clat,ax=ax1)

map.drawcountries(linewidth=0.1,color=[0.2,0.2,0.2])
map.drawcoastlines(linewidth=0.05,color=[0.2,0.2,0.2])
map.drawlsmask((230,230,230,255),(119,155,207,255))
meridians = arange(-180,210,30)
parallels = arange(-90,120,30)
map.drawmeridians(meridians,linewidth=0.1,dashes=[1,0],color=[0.2,0.2,0.2])
map.drawparallels(parallels,linewidth=0.1,dashes=[1,0],color=[0.2,0.2,0.2])
pcx,pcy = map(clon,clat)
map.plot(array([pcx]),array([pcy]),'ro',linewidth=1,markersize=5,markeredgecolor='r')
map.drawmapboundary(color='k',linewidth=2.0)

savefig('testfig.pdf')

close('all')

testfig.pdf (83.6 KB)