"One or more virtual hard disks, CD/DVD or floppy media are not currently accessible."
My virtual machine becomes inaccessible. Details show this error:
Could not find an open hard disk with UUID {5bad2863-64d0-40a2-a394-7442e3a6adc7}.
Result Code: VBOX_E_OBJECT_NOT_FOUND (0x80BB0001)
This happens when a snapshot is removed, then another snapshot is made and the host computer crashes (e.g. freezes during hibernation). After this, there is a reference to a non-existing HardDisk in the configuration file "~/.VirtualBox/VirtualBox.xml". This needs to be updated with the real value. The last working situation can be found in the log file (e.g. "~/.VirtualBox/Machines/<...>/Logs/VBox.log")
00:00:01.330 [/Devices/piix3ide/0/LUN#0/AttachedDriver/Config/] (level 6)
00:00:01.330 Format
00:00:01.330 Path
00:00:01.330 Type
00:00:01.330
00:00:01.330 [/Devices/piix3ide/0/LUN#0/AttachedDriver/Config/Parent/] (level 7)
00:00:01.330 Format
00:00:01.330 Path
00:00:01.330
00:00:01.330 [/Devices/piix3ide/0/LUN#0/AttachedDriver/Config/Parent/Parent/] (level 8)
00:00:01.330 Format
00:00:01.330 Path
This shows reliably the structure (the snapshot and its parents are listed), so it can be reconstructed by editing the XML file accordingly.