Q: Mountain Lion/Mavericks 'breaks' wifi base station - Snow Leopard works fine

Greetings all,

(Tried this in the OSx forum with no answers. Hopefully better luck here.)

I've been reading my way toward blindness through countless threads, here and elsewhere, from countless people, having problem with Mountain Lion and Wi-Fi these last few days, but some are using Airport, some are using third-party Wi-Fi routers, some aren't really specifying what they're using, so I thought I'd be as specific as possible about my situation - and add the fact that everything is still working fine if I boot into an old backup using Snow Leopard.

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So here's the situation. I have a Intel Mac Mini which I use as a Wi-Fi base station for a Intel PowerBook Pro and an iPod 5. The Mini has been running Snow Leopard, and the PowerBook had been upgraded to Mountain Lion a few months ago. Things were still working fine at that point - the PowerBook's shift from SL to ML didn't affect its connectivity as a 'receiver' at all. This past weekend however, I finally upgraded the Mini to Mountain Lion as well (so that I could install the current version of Adobe Lightroom) and lost my Wi-Fi Internet access.

When I turn Wi-Fi on at the PowerBook, the Mini's network is visible, and I get the solid Wi-Fi fan showing a full connection, but I cannot access the Internet (indicated by the exclaimation point inside the fan for the first few seconds). The same is true on the iPod - I get the checkmark showing that I'm connected, but when I try to access any Internet services will get a pop-up box telling me that the Internet is not connected.

After going through pages and pages and pages of people struggling with similar issues on sites like this, and following suggestions like deleting my preference files changing IP addresses etc. I got no further. But since I had cloned my hard drive just before the upgrade from Snow Leopard to Mountain Lion (thank you SuperDuper), I can reboot into Snow Leopard, and everything still works fine. With that advantage, I copied and re-created EVERY SINGLE preference in the system preferences for Network and Internet sharing* from the Snow Leopard into the Mountain Lion system. (I even went so far as to create a network in Mountain Lion's prefs. with WEP encryption instead of the newer WPA just in case that would make any difference at all.) But even with identical settings on the Mini regardless of booting into Snow Leopard or Mountain Lion, Mountain Lion remains the same - no problem connecting with the network, but complete inability to access the Internet. Then, hoping against hope that an upgrade to Mavericks might reset things into some sort of working mode, I tried that - but no better result.

(*) I note that the wifi heading in the preference panes has changed from "AirPort" in Snow Leopard to "WiFI" in Mountain Lion and Mavericks, but I'm assuming that's just a change Apple made in its terminology to avoid confusion with the external AirPort options.

I would appreciate any suggestions any of you could give. And I would ask that you specify whether any suggested changes are to be made on the originating Wi-Fi station (in this case the Mini), or the receiver (in this case the MacBook). Many of the threads I've read to date can be confusing simply because they're not specifying on which machine any suggested changes need to be made, and while I'm sure there's nothing that needs to be changed at the MacBook, please specify if I'm wrong.

Thanks again,