I googled all over this topic and I see I'm not alone on this one. Does anyone know why PHP Nuke won't save my Prefrences. It does everything perfect except saving prefrences.

I suggest you reading this => http://64bit.us/article83.html
and then return to phpNuke 7.6 =) then we'll talk.
I will not give support on either nuke 7.7 or 7.8, maybe someone else does but not me. I don't invest time in stuff that is broken when it arrives, in stuff that goes backwards every release and that breaks my Modules.

Sorry,
Mighty_Y

I found the problem. I replaced all occurences of nuke in the database script to a new prefix, and changed the prefix in my config file. I must have replaced one that should not have been replaced.