Apple Launches New EFI Update 2.9.1 For 2011 MacBook Air to Solve Installation Problems
The update, originally released on July 15 to address sleep/wake issues, caused some MacBook Air machines to shut down completely for several hours. On other machines, the update simply refused to install. Today's re-released software, labeled 2.9.1, presumably fixes these issues, allowing the update to be properly installed.
The MacBook Air EFI Firmware Update 2.9.1 is available in the Mac App Store for 2011 MacBook Airs and can also be downloaded from the Apple Support site.