Folks, wanted to recap this as I am finding the problem much more broad than my original post (here: https://discussions.apple.com/message/19123146#19123146). Here's my setup:
- MacBook Air 13", Mid 2011
- Mountain Lion
- Wifi Problems, cannot connect to open wi-fi and Sprint hot spot.
- CAN connect to Time Capsule (at least I could before I started futzing with my setup while on the road)
here's what I've done so far:
- Reset SMC
- Zapped PRAM
- Reduced MTU to 1300
- Set hotspot to 802.11g only
- Set IPv6 to Local-link only
- Set up a new user account, no connection there either
- Repair disk
- Repair disk permissions
- Removed WiFi in networking control panel and re-add.
- Remove the network from control panel AND remove keys from Keychain
What I have not done but will try later:
- Reinstall ML
- Disable WMM
- ML seems to think there is a connection to the wi-fi, but it can never get an IP address
- Using a static IP on the network doesn't help the problem
- My hotspot never really registers the MBA as a connection
OK, the only thing that has solved my issue is a fresh ML install from the rescue partition. I used my wired connection for the install just in case something was horky with the Wifi.
Your mileage may vary!