Updated – 18 April 2012 - Problem seems to have gone now, between my fix and the Apple update on 5 April.

Updated – 5 April 2012 – Apple released an update for iMac titled ‘iMac Wifi Update’ today, which I’ve now updated my system with. Hopefully this will completely fix the issue.

Original Post: Since upgrading to Lion (via App Store) I’ve had this issue on my iMac where wifi connection is always lost when come back from Sleep and have to reconnect – which didn’t happen in previous OSX versions. Annoying but the fact the workaround was simple meant I never looked into getting a fix, until today…

My fix was pretty simple – worked for me, maybe won’t work for everyones setup/situation:-

– System Prefs / Network / then Turn WiFi off
– Press Advanced button, it will probably show your usual WiFi network in Preferred Networks list
– Delete your usual WiFi network in this list (make sure you have your connection details/password first!!!)
– Press OK and will then need your System password to ok the change

After this, it then worked fine, auto-connecting after each Sleep.

So far tested with a short Sleep (2 mins) and a longer Sleep (about 30 mins)
Haven’t yet tested with an ‘overnight’ sleep.

I’ve added this info to Apple Support forum, as there seemed to be a lot of people with the same issue (20 pages worth!)

https://discussions.apple.com/thread/3193100?start=285&tstart=0