"The selected virtual machine is inaccessible. Please inspect the error message shown below and press the Refresh button if you want to repeat the accessibility check." After saving states of all virtual machines of VirtualBox running on Mac, rebooting the Mac host without any issue. Then it was a big surprised that all virtual machines are inaccessible. Not only the virtual hard disks, but all the virtual machines files.
This case was caused by previously renaming the external SSD storing the virtual machine files. After renaming back to original disk name, still have to
- Remove the virtual machines and Add them back to VirtualBox by going to the VirtualBox application top bar
- Choose Machine -> Add
- Select the file with .vbox (that's the virtual machine file, not the .vdi or .vmdk). In case, the there's unexpected quit of VirtualBox, the .vbox may be corrupted, then it is necessary to rename the .vbox-prev to .vbox
- It is not easy to recognise that the issue was caused by renaming the path (in this case, the SSD disk) of the virtual machine as not until restarting VirtualBox, it is not observed there is any error on the virtual machines.
- Even after renaming back the path to the original one, VirtualBox still shows inaccessible virtual machine. The suggested solution of clicking the Refresh button located at bottom left cannot fix the problem. (Don't know why Oracle is so stupid to suggest this!)
- The Machine -> Add appears only at the top bar of VirtualBox application, but not appear at the top bar of Oracle VM VirtualBox Manager
- It is easy to misinterpret the error message that it was due to inaccessible storage and it would be tempted to create new VM and access the same original storage, but it is not good in the sense that the virtual hard disk is located under the old VM's directory.
- Mac users always have TimeMachine backup for the virtual machines, in such case restoring the VM directory is wasting time.
OS X 10.12.1