openerp-server fails to install/run in ubuntu 13.04

[Peter Chibunna]

OpenERP7.0 was running perfectly well when I was on Ubuntu 12.10. but after I upgraded my o.s. to ubuntu 13.04, openerp wouldn't start again. The traceback is pasted below

Traceback (most recent call last):
  File "/usr/local/bin/openerp-server", line 4, in <module>
    import pkg_resources
  File "build/bdist.linux-i686/egg/pkg_resources.py", line 2603, in <module>
    line, p, specs = scan_list(VERSION,LINE_END,line,p,(1,2),"version spec")
  File "build/bdist.linux-i686/egg/pkg_resources.py", line 666, in require
    continue # try the next older version of project
  File "build/bdist.linux-i686/egg/pkg_resources.py", line 565, in resolve

pkg_resources.DistributionNotFound: PIL

I tried to re-install it, The error message was still pointing to PIL not found. But I could verify that PIL is correctly installed because I can import PIL from python shell. I can also import Image; I can also manipulate photos using PIL.

But openerp7 still shows me the traceback I pasted above.