I have a mid 2011 with Lion and have recently bought an airport express router which works, as far as I know, fine. My phone, pcs etc connect fine. So does my iMac. However, airport keeps dieing! It stays on, but not connected to anything. It doesn't even see any other networks ( of which there a small number). Switching it on and off makes no difference. The only fix is to restart the iMac and then it works fine, until it suddenly dies again. Anyone else had this issue before?