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People have published a variety of fixes for wireless connections dropping in Lion, and even a keepalive scripts that helps many users maintain a connection in some of the stubborn cases, but some Mac OS X Lion users continue to have problems with their internet connection failing. After diagnosing another MacBook with wireless stability problems post-Lion, I found a solution that hasn’t failed yet and doesn’t require any of the other tips.
Before proceeding, make sure you have done the following:
After you’re positive you’re on the newest version of OS X and have all software updates applied to the Mac in question, proceed with the solution:
Add a New Network Location & Renew DHCP Lease
You should now have a stable wireless connection under Mac OS X Lion 10.7.2.
For most users the wifi stability issue was resolved with installing the latest OS X Lion updates, but in some cases is seems that old network connection profiles brought the problem forward for to the newest OS update. You may have to enter the wireless network password again before you can connect to the router, if you don’t know that be sure to find it out from someone who does before troubleshooting with this tip.
All Credit for this Howto go to OsXdaily.com