After transferring our openERP 5.0.16 server to a new host, we are getting this error message while trying to add an attachment through the web client :
a class that defines __slots__ without defining __getstate__ cannot be pickled
The problem was that the default version of cherrypy was 3.2.2 and the web-server seems to have needed 3.1.2.
You can useĀ ‘easy_install cherrypy==3.1.2’ to install the required version and now the web-server works fine.