Netbackup 8.1.2 Web GUI is not responding

[Kalm]

Not able to lauch NetBackup 8.1.2 web console - 

https://nbu-server-hostname/webgui/login

OR

https://nbu-server-ip_address/webgui/login

Error:

The webpage cannot be found

There is a problem with this website's security certificate (Alert),... if we continue to this website (not recommended) with this warning:

HTTP 404 not found error appeared!

[Amol_Nair]

You seem to be using the incorrect URL. The Web UI URL also includes port 1556.. It should be something like the below 

https://nbu-server-ip_address:1556/webui/login