Comment 7 for bug 454436

As noted by Miguel Tadeu, the openerp user has to be logged out first, otherwise dpkg will keep throwing errors.
So to uninstall openerp-server on my Ubuntu 10.10 32bit desktop, I ran :
$ sudo skill -kill -u openerp

and then I was able to remove openerp-server using:
$ sudo apt-get remove openerp-server

For details, see "man skill" or http://www.cyberciti.biz/tips/howto-linux-kill-and-logout-users.html

P.S. I did not need to stop the openerp-server service manually, apt-get took care of it during the removal process. However, if you need to stop the openerp-server process, you can do so manually using be4truth's instructions above.