This thread saved my life!
Last night I decided to update the BIOS of my GA-P55M-UD2 from F5 to F10. My main goal was to get sleep working, so I also replaced my DSDT.aml with the one tony supplied.
After rebooting, all my hardware was not compatible with my 10.6.2 installation. I proceeded to repair my /E/E extensions (once again) and rebooted, graphics and sound was fixed but USB drives were showing different icons (yellow instead of grey) and my iPhone wouldn't charge when plugged into my Apple keyboard like usual.
So I used multibeast to install the Gigabeast for my mobo, along with the USB kexts. After rebooting, everything was back to normal again.
Except, iTunes would not sync with my iPhone, or download any apps from iTunes Store. It kept giving me the -50 error, no matter what I did. It was also asking me to "Authorize" my computer again, which made no sense.
After looking around a lot and trying different things, I finally found this thread (by luck, really. it was #8 from the top of my google results).
After following the instructions here to reset my network preferences with that sudo rm command, rebooting, then reinstalling my wireless card drivers, iTunes syncs again!
I had no idea that the Mac and iTunes was so very dependant on something seemingly as insignificant as network settings. But ya learn something everyday dont you?
Anyway thanks guys, I really appreciate you.