This 404 error means that something is missing.
If you had a plugin installed and you removed it, then re-installing it will most certainly fix the problem. Remember that if you change the list of plugins in the /etc/snapwebsites/snapserver.conf file, you have to restart the server for the change to be taken in account.
If you are a programmer and you get this error and you know for sure that the plugin is loaded (you tried to restart and made sure that the plugin name appears in the snapserver.conf file or in the sites parameters,) then the next thing to look into is whether you implemented the proper functions for that plugin.
For example, if the plugin creates pages (i.e. the e-Commerce plugin creates the /products page, for example) and that page does not force a specific owner, then the page has to be handled by that plugin. This means you must have a main page generation function:
virtual void on_generate_main_content(content::path_info_t& ipath, QDomElement& page, QDomElement& body, const QString& ctemplate);
This is a virtual function defined in the path_execute class (defined in the path plugin.) This function is required if a plugin defines its own pages. It may be programmed to simply call the output function of the same name to display the page.