Quick answer: Failed to open a session for the virtual machine is VirtualBox’s general “this VM won’t start” message. The real cause is in the Details part of the dialog, usually a code such as E_FAIL (0x80004005), VERR_VMX_NO_VMX or VERR_NEM_NOT_AVAILABLE. The most common fixes are: right-click the VM and choose Discard Saved State, turn on VT-x or AMD-V in the BIOS, stop Hyper-V from holding the CPU’s virtualization, or fix a missing USB controller or network adapter in the VM’s settings.
Applies to: Oracle VirtualBox 6.x and 7.x on Windows 11 and Windows 10.
In this guide
What the error means
When you start a virtual machine, VirtualBox opens a “session” that locks the VM and launches its process. If anything stops that launch, you get Failed to open a session for the virtual machine [name]. The message on its own doesn’t say why.
Select Details (or the small arrow) in the error dialog. Look for the lines that start with Result Code and any text in capitals that starts with VERR_. That code tells you which fix below applies.
Match the error code to the fix
| You see in Details | Likely cause | Go to |
|---|---|---|
E_FAIL (0x80004005) after the PC crashed, slept or was shut down with the VM running | Damaged saved state | Fix 1 |
VERR_VMX_MSR_ALL_VMX_DISABLED, “VT-x is disabled in the BIOS”, “AMD-V is disabled in the BIOS” | Hardware virtualization is off | Fix 2 |
VERR_VMX_NO_VMX, “VT-x is not available”, VERR_NEM_NOT_AVAILABLE | Hyper-V or another hypervisor is using VT-x | Fix 3 |
| “Implementation of the USB 2.0 controller not found” | USB 2.0/3.0 enabled without the Extension Pack | Fix 4 |
| “Nonexistent host networking interface” or “Could not find Host Interface Networking driver” | The VM’s network adapter no longer exists | Fix 4 |
supR3HardenedWiReSpawn, exit code 1, driver errors after a Windows update | Damaged or outdated VirtualBox install | Fix 5 |
Fix 1: Discard the saved state
If you closed the VM with Save the machine state, or Windows shut down or crashed while it was running, VirtualBox tries to resume from a saved state file. If that file is damaged, the VM won’t open.
- In VirtualBox Manager, right-click the VM (its status shows Saved).
- Select Discard Saved State and confirm.
- Start the VM again. It boots fresh, as if it had been powered off.
This loses whatever was open inside the VM at the moment it was saved, but not the files saved on its virtual disk. If the VM shows Aborted instead of Saved, just try starting it again.
Fix 2: Turn on VT-x or AMD-V
64-bit guests need the processor’s hardware virtualization. To check whether it’s on, open Task Manager (Ctrl + Shift + Esc), go to Performance > CPU and look at Virtualization.
If it says Disabled, restart into the BIOS/UEFI setup (usually F2, Del or F10 at startup) and enable Intel Virtualization Technology (also called VT-x or VMX) or, on AMD, SVM Mode / AMD-V. Save, exit and try the VM again. Our Not in a hypervisor partition guide has more detail on where makers hide this option.
Fix 3: Stop Hyper-V from blocking VirtualBox
If Task Manager shows virtualization as Enabled but VirtualBox still says VT-x isn’t available, Windows’ own hypervisor is probably holding it. It runs when any of these are on: Hyper-V, Virtual Machine Platform (used by WSL 2), Windows Sandbox, or Memory integrity under Core isolation.
You have two options:
- Keep Hyper-V and let VirtualBox share it. Current VirtualBox versions can run on top of the Windows hypervisor (through Windows Hypervisor Platform). Update to the latest VirtualBox and turn on Windows Hypervisor Platform in Turn Windows features on or off (
optionalfeatures). VMs may run slower this way. - Turn the Windows hypervisor off. In an administrator Command Prompt run the command below and restart. This stops Hyper-V VMs, WSL 2 and Windows Sandbox from working until you turn it back on with
bcdedit /set hypervisorlaunchtype auto.
bcdedit /set hypervisorlaunchtype offIf you also need to switch off Memory integrity, go to Windows Security > Device security > Core isolation details and turn Memory integrity off, then restart. This lowers your PC’s protection, so only do it if VirtualBox can’t work any other way. If Windows Security won’t open, see Windows Security not opening in Windows 11.
Fix 4: Fix USB and network settings
USB controller not found: the USB 2.0 and 3.0 controllers need the Oracle VirtualBox Extension Pack (on most VirtualBox versions). Either install the Extension Pack that matches your exact VirtualBox version from the official download page, or open the VM’s Settings > USB and choose USB 1.1 (OHCI) Controller or untick Enable USB Controller.
Network interface missing: this happens when a VM uses Bridged Adapter or Host-only Adapter and that adapter was removed or renamed, for example after a VirtualBox or network driver update. Open the VM’s Settings > Network, reselect the adapter in the Name list, or set Attached to to NAT to get it running.
Fix 5: Update or repair VirtualBox
Errors that mention supR3HardenedWiReSpawn, VBoxSup or a VM that closes with exit code 1 often mean VirtualBox’s drivers are damaged or don’t match a recent Windows update. Download the latest version from the official VirtualBox site and install it over the old one; your VMs stay in place. If that doesn’t help, uninstall VirtualBox, restart, and install it again with Run as administrator.
Security software that blocks or scans VirtualBox’s processes can also cause these errors. Check its quarantine or history for VirtualBox files.
Still failing? Read the log
Right-click the VM and select Show Log (VirtualBox 7: Log Viewer). Scroll to the end of VBox.log and look for the first line containing VERR_ or error. Searching that exact code usually leads to the cause. Also check that the VM’s virtual disk still exists where VirtualBox expects it, in File > Tools > Virtual Media Manager (older versions: File > Virtual Media Manager).
Note that Could not create the Java Virtual Machine is a different error from Java, not VirtualBox.
Related guides
- Not in a hypervisor partition (HVP=0) in VirtualBox: fixes
- Windows Security not opening in Windows 11
- Could not create the Java Virtual Machine: how to fix it
Official sources: for more detail, see these pages:
- Oracle VirtualBox documentation: Troubleshooting
- Microsoft Support: Enable virtualization on Windows
- VirtualBox: official downloads and Extension Pack
Frequently asked questions
Will Discard Saved State delete my virtual machine?
No. It only throws away the paused memory snapshot. The VM, its settings and its virtual disk stay as they are.
Do I have to uninstall Hyper-V to use VirtualBox?
Not always. Recent VirtualBox versions can run alongside Hyper-V through the Windows Hypervisor Platform, though more slowly. Turning the hypervisor off with bcdedit is the fallback if that doesn’t work.
The error started after a Windows update. What should I do?
Update VirtualBox to the latest version first. Major Windows updates sometimes turn Memory integrity or Virtual Machine Platform on, so check Fix 3 too.
Does running VirtualBox as administrator help?
Usually not. Mixing an elevated VirtualBox window with a normal one can even cause its own errors, so use administrator rights only when installing or repairing VirtualBox.
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