I downloaded a module called product_by_supplier to my Ubuntu directory /opt/odoo/odoo/addons and unzipped it there. After trying to access the Odoo server through web browser I got following:
http://i.imgur.com/o45MQVk.png
I then removed the .zip and the unzipped folder from /opt/odoo/odoo/addons, but with no difference.
The log file shows:
http://i.imgur.com/zF02F7l.png
and the server:
http://i.imgur.com/HLzI9LD.png .
The server error looks like your real problem. Odoo is telling you that there is already an application running on port 8069 (perhaps another Odoo?). This is the reason that you cannot launch this Odoo.
What did I do to make this happen and what do I do to make Odoo run again?
and also remove the zip file from addons directory.
Killing the process did not fix the problem. It seems that I've run the server on a Ubuntu user named "odoo", and I'm not able to log in to that. So when I try to connect to the server it says that there is no database user with the same name as the user that I run the server on. Is it possible that when I added a .zip and a new folder to /opt/odoo/odoo/addons, some config file got messed up? Since now it can't find this web.assets_backend thing.