Scenario: You have a new HP Color LaserJet Pro MFP 4302. It has been powered up and assigned (manually or by DHCP) an IP address which already has a DNS address associated with it. After finding the label with the initial admin password you try and access the Embedded Web Server (EWS) via your web browser. You use the DNS address for this.
What you get after a couple of seconds is a HTTP 403 error.
Try accessing the page using the IP address – it should work. The problem seems to be that if the printer thinks its DNS name is different from the actual address it breaks the EWS.
In this particular case, it was fixed by going to Network→Network Settings→Identification and changing the Host Name to be the same as in the DNS server. Then (after some refreshing of pages and re-logging in) you can use the DNS address to access the EWS as expected.