I also face the same problem. Everything was working well before Sunday. All my devices can be connected to my unifi router. All of a sudden, my HTC Desire HD, iPad and Acer laptops cannot detect the wifi anymore. My neighbour's unifi can be detected. My brother's iPhone 3G and 3GS, Asus laptops can connect to my wifi. Strange but true. I have changed the settings to 20mhz and also wireless b/g/n. Still the same outcome. Please help.