Some things to try...
Make a New Location, Using network locations in Mac OS X ...
System Preferences>Network, click on the little gear at the bottom next to the + & - icons, (unlock lock first if locked), choose Set Service Order.
The interface that connects to the Internet should be dragged to the top of the list.
Instead of joining it from the list, click the WiFi icon at the top, and click join other network. Fill in everything as needed.
I have the same problem: After waking up the iMac the wifi connection is lost, and the iMac is no longer able to see any networks around. Restarting is the only thing that'll get the wifi connection back.
There is a lot of talking about changing the "location", pulling the WIFI connection to the top of the list in the network setting, resetting the SMC, fixing the WIFI channel instead of using "automatic", and lately: installing the 10.7.4 combo update (1.4 GB download), but... nothing helps!
Apple needs to correct this NOW! :-/
I'm glad that other people are experiencing this, too! When I called Apple Support last night, the representative continued to tell me it must be a hardware issue and that my only solution was to go into an Apple Store and have it serviced. She refused to believe that it was an OS X issue and wouldn't even transfer me to an OS X support agent!
Since upgrading to 10.7.4, my iMac has dropped its connection to two of my wireless networks, and can't even DETECT my third!! What a crock of crap, Apple! Do you all even beta test OS X before a version release anymore?!
If this was an iPhone issue, you'd believe in a second they'd have an OTA patch released same day!
I spoke to an Apple Senior Advisor at network/wifi tech support last night. They are aware that this is due in large part to 10.7.4 update. The advisor said he has received several calls about this and has escalated the issue to the engineers. He also said he didn't expect to know anything or have an answer until Wednesday. I hope they have a fix for this by Wednesday.
Well i guess all iMac's (Mid 2011) did fail at the same time!
Possible HW failure, thats a stupied answer! (It just shows the quality of the support you get.)
The 10.7.4 update (even after trying the Combo update) introduced this problem on my iMac (Mid 2011) and AirPort Extreme. it's the iMac WiFi interface that fails and stops working and you need to reboot the iMac to get it up and running again, all other devices still works aginst the Airport Extreme (Latest Generation) iPad's, iPhones, PC's and so on.. So don't tell me there could be interference or something else!
Apple needs to take some action now, please announce that there is a bug or failure with the WiFi and 10.7.4 update, even 10.7.x had failures on iMac's and WiFi when suspend was enabled!
Please fix this problem now, once for all! (And test it on an iMac mid 2011 before releasing it)
So I haven't necessarily had an issue with the wifi dropping (frankly haveb't used it enough since the last update) but rather with the machine not "auto connecting" to my network on boot. As you know, 10.7.4 adds the option to uncheck the "reopen windows next logon" feature. Well I found a direct correlation between having this checked vs. not checked.
When checked, the machine automatically connects.
When not checked, I have to go find my connection in the wireless interface.
It's as if the wifi service is being considered a program and not reopening when the option is not checked.
Mind you I'm very new to MACs; however, this seems awfully coincidental to me.
Possible short term fix:
Same issue. Mid 2011 iMac. Updated to 10.7.4 and wifi dropped. The iMac could see any SSID until it was rebooted. My MacBook Air, iPad and iPhone all fine.
I went to Apple tech support and like others was faced with a slippery resistance to the idea that this was anything to do with 10.7.4.
Eventually it was suggested I reinstalled Mac OS (switch off, switch on with cmd and R keys held down. Then follow the process. I wasn't hopeful but was compliant. Imagine my joy when, on coming back to me my iMac asked if I wanted to update to 10.7.4. Of course not!
So reinstalling Mac OS takes you back to 10.7.3. So far so good. Will keep you posted.
Still hoping fpr a proper fix from Apple but they don't seem to be taking seriously
in contrast just updated Omin Group's Omniplan (BTW this is great software for the Mac, check out their offering if you haven't). The update notes:
"It seems as if our fix to the Task: Schedule Inspector in 2.1.1 actually caused more widespread crashes. We've rewritten this code in a more robust fashion and have not seen this problem reappear"
Owning and fixing the problem - Apple guys please take note!