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Found a SOLUTION that works for me!!!!

I have a Macbook, and was experiencing the EXACT annoying problem. I called the apple support phone number and they gave me a solution to the problem and it finally works again!

1. Go to system preferences and open or click Network

2. On the Wifi tab, click on Advanced button near the lower right corner

3. On the Wi-Fi tab go to the Preferred Networks box where it lists the networks your computer knows to connect to

4. Now delete all of the networks that you do not recognize, especially ones that may be in your apartment building or that your computer may be in range of. Make sure that your network is at the top of the list. You can drag them. The tech person said it was ok to have a couple other ones, but to make sure that mine was at the top of the list.

5. CLick OK then apply. now try it out and see if it worked

At first Safari gave me the same error message but about 3-5 seconds later it automatically loaded up my homepage. Then after 2 more times of shutting or putting my computer to sleep to test it, it started loading my homepage like normal again. I really hope this works for you because I know how enraging the problem is :mad:!
 
I don't know if it's a "bug" or not, but I noticed that once I was connected with Snow Leopard, I never had to reconnect again. With Lion, every time my computer comes back to life, I need to reconnect to the network. I don't mind though, because it's a matter of move the mouse and enter. It's much quick than what I was used to on a PC, that's probably why I don't mind haha. I can't tell if this is meant to happen or should be considered a bug though.
 
WIFI works perfectly on Windows 7 on my MBA. Sticking to that OS permanently until Lion gets fixed.
 
WIFI works perfectly on Windows 7 on my MBA. Sticking to that OS permanently until Lion gets fixed.


Mine stayed connected automatically with Snow Leopard to whichever network it knew around. Mine works once it's up and connects in a snap, but I can't tell if it's an issue that when it wakes up, I have to select and connect. This is a different situation than the OPs, but similar to someone who began gearing the thread towards this idea because the network I want is indeed set to default following the above instructions. Hmm.
 
Same issue

I have a similar issue. Bought new Macbook Air with Lion, then first noticed ocaissional problem with wi-fi on all computers. Upgraded new iMac to Lion few days later, problem continues even on other imac with Snow Leopard. Interestingly, Airport Utility will not detect any wireless devices when I have this problem, not my Time Machine or any of my airport expresses. After turning off Time Capsule for 15-30 seconds and restarting, everything works fine.
 
My iMac 27" is undergoing diagnostics by the technicians at the Apple reseller in my city. In the mean time, I decided to install Lion on a separate partition on my four year old macbook pro 15". This machine was also experiencing similar issues. So doing some more searching led me to this youtube video. http://www.youtube.com/watch?v=LjbKXYOGW3c
And I figured why not give it a shot. So I went into network preferences, deleted the wifi network on the pane on the left side by pressing the '-' button. Then I rebooted even though that step is not mentioned in the video. After booting back up again, I pressed the '+' button and re-added wifi connection and then re-connected to my wifi network. Lo and behold, I am now online from my Lion installation on my Macbook Pro!

The technicians called me to say that they couldn't find any issue with wifi on my iMac and I should pick it up. They said it has been pinging yahoo all night without any issues. So after I bring it back home, if it is still giving me issues, I will use this procedure on the iMac itself and report back.
 
Same problem here.

I noticed with Lion, if I put my MacBook to sleep (close the lid) and re open it, the wireless gets dropped. In SL it would automatically join back to the wifi.

The only way I can fix this in Lion is to goto the Wireless icon in the task tray and manually select my hot spot.

I wish there was a fix. I opened a thread for this because I got lost in the lion mess. Sheesh

I have the same problem with my MBP since installing Lion. When I close the open the MBP, sometimes it has trouble reconnecting. I notice that the Time Machine icon is spinning - the machine thinks it is connected or backing up maybe. The work around at this point is to turn Time Machine off, then turn WIfi Off/On via the icon in the command bar - or to go to network prefs and turn Wifi off/on
 
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