Cannot login to SonicOS web-based management interface via HTTP after upgrading to SonicOS 5.8

Beginning in SonicOS 5.8.1.7, HTTP access to the SonicOS web-based management interface is disabled by default. When running SonicOS 5.8.1.7 using factory defaults, the administrator can log into the management interface using HTTPS at https://192.168.168.168.
HTTP management is still allowed when upgrading from prior firmware versions, when already enabled in the previous configuration settings.

NOTE: HTTP management must be enabled when the firewall is being managed by SonicWall GMS via a VPN tunnel. This applies when using either a GMS Management Tunnel or an existing VPN tunnel.

The System | Administration page has a new Allow management via HTTP checkbox to allow the administrator to enable/disable HTTP management globally.