Are you wondering why lion says no mountable system ? You can not install any of the software and application on the Mac Lion system because of this error. You need to mount the dmg file of the software to any of the Mac drive and then install it in the system if the image is not mounted in the drive it is impossible to install. The answer for why lion says no mountable system can be that may be the dmg file is corrupted. You can try to get a fresh copy of the file but if it not working then the problem is with the drive. You may have to check it with the disk utility which can fix it. If the drive is not fixed then you have to format the drive which will also remove the content of the drive. You can restore the file with the help of time machine. If the time machine can not provide the backup then you have to use the Mac data recovery software which scans for the deleted file and then restore it finally. The restoration process is quite simple and you will get all the files which can be accessed then. So now when you know why lion says no mountable system then download the software.