My network and internet access are working OK. However, the Airport utility on my iMac says it can't find my Airport Extreme and the Airport Express [connected to my music system] that links to it. All my devices are connected to the Extreme using WiFi. Sometimes the Airport utility pops up on the iMac screen and then an unknown app asks for access to my keychain, which I deny. This has started happening since I updated the Express firmware a few weeks ago. I have Back to my Mac turned off. I can use the Airport utility on my iPad and both devices show up OK there, but not on my iMac. Also, everything looks normal from my wife's Macbook. So is it something on my iMac? The unknown app that asks for access has an icon of a locked padlock and something like a blade to the right of it. I can't find this icon anywhere.