Did you get your copy of PHP-Nuke 7.9 from phpnuke.org?

I cannot help you with 7.9, but I do know that 7.9 has bugs and is not a good version. The best version out there so far is 7.6 patched with chatserv's patches.

Some people will recommend Raven's distro, but IMO it has too many options that I do not want. I prefer a clean stock version and then install any add-ons myself. Better learning curve.