Possibly incorrect pass. Check with your isp for the correct way of logging in or use the default as suggested on the Portforward site.
Your ISP login & router login will not necessarily be the same. There is probably a default login for it. I have mine bookmarked via my browser for auto-login so I can't remember much about it but I probably have a note about it somewhere both on the computer & hard-copy. If you've never set it for yourself, then there will be a default log in most likely.

Depending on the device, you can reset the login. You basically reset the device which kills any memory of settings within it.