OS X Lion installer 'cannot be verified' after download
One problem that some people are having with the new Mac OS X Lion release is that the downloaded installer appears to be getting corrupted during the download process. After purchasing and downloading the installer, some find that the system will claim that the software cannot be verified after it has been launched.
Multiple users have confirmed that the MD5 checksum for the installer disk image is "b5d3753c62bfb69866e94dca9336a44a," and you can check this on your downloaded installer by running the following command in the Terminal (copy and paste it):
/sbin/md5 "/Applications/Install Mac OS X Lion.… Read more