Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
Apple seeds OS X Lion 10.7.2 Beta 3 –
Apple now released the latest software OS X Lion 10.7.2 Beta 3 to developers earlier today. They also released 10.7.2B3 (11C43),iCloud Beta 9 and iPhone Beta 3, all of which are available on Apple’s Developer site. Most of the updates include AirPort, AppKit, GraphicsDrivers, iCal, iChat, Mac App Store, Mail, Spotlight and Time Machine.