Are you interested in causes of no mountable file systems errors ? If you have created a new partition or have an external drive in which lots of data is saved and it needs to mounted for performing any kind of data transfer operation. But you are not able to do so because of the drive is not mounting to the Mac system then you must be wanting to know the causes of no mountable file systems errors. The probable causes of this issue can be that the drive has not been connected well, it has any unknown file system, the drive partition has been corrupted or the drive is infected by virus. In such cases you may have to format the drive which will remover the causes of no mountable file systems errors but also it will erase all the contents of the drive. You can restore the lost files with the help of the time machine backup utility but if it fails because of any reason you can try Mac data recovery software that effectively scan the Mac drive and shows the scan result in the preview. Select and restore the files you need and you no longer have to bother about the causes of no mountable file systems errors.