Mohammed Mahgoub (mmahgoub)

One of the methods used to add an extra modules directory is through the command line which goes something like this in Windows Powershell:
 

The problem arises when you don't have any modules inside that directory, the terminal will throw the error "odoo-bin: error: option --addons-path: The addons-path 'C:\\Users\\mmahgoub\\Desktop\\addons' does not seem to a be a valid Addons Directory!" and the odoo instance will fail to run.

This is because there are no valid existing add-ons available to install, as soon as you put a valid add-on which contains __init__.py, __manifest__.py inside specified directory the run command will work as expected.