vboxmanage locked write

$ vboxmanage list hdds

UUID:        42bc1333-82ae-44ee-9fe8-40e6fffac34d
Parent UUID: base
Format:      VDI
Location:    /mnt/test10/vbox/ramdisk3.vdi
State:       locked write
Type:        normal

$ vboxmanage closemedium disk /mnt/test10/vbox/ramdisk4.vdi
VBoxManage: error: Medium '/mnt/test10/vbox/ramdisk4.vdi' is locked for writing by another task
VBoxManage: error: Details: code VBOX_E_INVALID_OBJECT_STATE (0x80bb0007), component Medium, interface IMedium, callee nsISupports
Context: "Close()" at line 1195 of file VBoxManageDisk.cpp