AttributeError: Nonetype with openerp-client

I installed openerp-server 5.0.6-2 and the openerp-client. I successfully opened the client and created a new database. Then I quit the client and installed the medical add-on (medical_0_1.1). Subsequent attempt to launch the openerp-client gave the error:

Traceback (most recent call last):
  File "./openerp-client.py", line 138, in <module>
    win.sig_login()
  File "/usr/local/lib/python2.6/dist-packages/openerp-client/modules/gui/main.py", line 1051, in sig_login
    res = l.run(dbname=dbname, parent=self.window)
  File "/usr/local/lib/python2.6/dist-packages/openerp-client/modules/gui/main.py", line 538, in run
    res = self.refreshlist(None, combo_db, entry_db, label, url, but_connect)
  File "/usr/local/lib/python2.6/dist-packages/openerp-client/modules/gui/main.py", line 494, in refreshlist
    if _refresh_dblist(db_widget, entry_db, label, butconnect, url):
  File "/usr/local/lib/python2.6/dist-packages/openerp-client/modules/gui/main.py", line 380, in _refresh_dblist
    entry_db.hide()
AttributeError: 'NoneType' object has no attribute 'hide'

I purged the openerp client and reinstalled it but this did not correct the error.

Can anyone help?

Since I could not make progress with the OpenERP client because of the above problem. I decided to install the Web client. Though the process was long but I finally succeeded. I would still love to use the OpenERP client if anyone can solve the problem I had above, which does not seem to be limited to me from reading the comments on the installation guide page.