Oh dear, one of
those guides. The problem with them is they install a whole host of nonsense only useful to pirates (and I guess legitimate backup users, but the number of pirates greatly outnumbers them sadly), without the person installing (you, in this case) really understanding what they're doing.
It's so much better to learn what stuff actually does and decide for yourself what you want to install. Although I understand that takes time and not everyone wants to spend time doing that.
Anyway, if you go into priiloader and go to settings then system menu hacks, you should see a hack called something like "block online updates" which will be enabled; disable it, then system update should work. After that, try homebrew again.
Also, I want to check: what homebrew are you loading? (Just making sure it isn't something that relies on a cIOS like a backup loader or WAD installer, in which case the "problem" is probably a stubbed IOS249, and we won't really give you any help seeing as we don't support that sort of thing here; if on the other hand you're loading stuff like emulators or WiiMC or homebrew games or whatever, we'll do all we can)