I recently clean installed Mountain Lion to my mid 2011 iMac, and ran into a frustrating issue when joining my Wi-Fi network. All my other Apple devices have no trouble accessing the same wifi, except this very iMac. The typical error message is either "See network administrator" or "Connection time out"
I did try to update the iMac to the latest (10.8.2 at the time of writing), and I still can't join the WiFi.
On the same iMac, if I reboot and boot into ubuntu Live CD, I was able to join the WiFi using the same internal wireless card. It leads me to think that something is off with Mountain Lion.
The router currently uses WPA2. I also did a wifi analysis and picked a channel that is least used by nearby routers.
I also spent quite sometime doing research. I cleaned up the Keychain-access, and I removed and re-added the network within the Wi-Fi network settings. I also make sure that SSID of my router has no "-" or any other weird characters. I also reset my router a few times, but it didn't help
The iMac came with Lion, and the WiFi connection to the same router wasn't all the stable, but at least I was able to connect. With Mountain Lion, nada no dice, not even connecting once
I am running out of ideas, and the current workaround is to rely on wired cable directly to the router. Or if I really want a stable wifi on this iMac, ubuntu. Any suggestions are greatly appreciated.
Best Answer
I faced a similar issue on my MacBook Pro with one particular WIFI connection. It was giving me the "Connection time out" error message.
I was able to workaround it by:
1) Removing the WIFI connection: System Preferences > Network > WIFI > Advanced > Select the relevant connection and click the "-" sign > Click "Show All" or close the window.
2) Adding the connection manually: System Preferences > Network > WIFI > Advanced > Click on the "+" sign > Enter the connection settings manually.
This has worked for me and that particular connection never gave me issues afterwards.
Hope this helps.