When Lead registration from external resources is not working

If you have followed necessary steps of Web to Lead form setup, pasted the generated code to the website, and leads are not being registered, than you should check the system settings ‘Username for Registering Leads from External Resources’ and ‘Password for Registering Leads from External Resources’. :

These settings are required for requests’ to the service authorization.  Respectively, all the incoming leads will be created on behalf of the specified user.

In case if correct username / password won’t be set, the requests will be rejected as unauthorized, and leads will not be created.