You have encountered Error 20 on Mac and want to know Causes and solutions of Mac Error Code 20. The Mac error 20 is an i/o system error due to which you can neither save any new file on the drive nor you can access any file from the drive. The causes of the error 20 can be any corruption in the Mac hard drive or the operating system is unable to perform any operation on the drive. You should first use the in built disk utility to check the hard drive and fix any minor corruption issue. If the disk utility is unable to fix the corruption then here are more Causes and solutions of Mac Error Code 20. You then have to check the operating system and if required reinstall it. When it is done you will notice that the files of the Mac drive has been erased, you can get it back by using time machine or you can try Mac data recovery software . If you have the other backup source then don't worry otherwise the software will recover and restore all the lost files. Now you know the Causes and solutions of Mac Error Code 20, so download the software and fix it.