Ubuntu VM on Windows10 quit working

[JPV]

Hello,
I work on a Windows 10 home, all updates installed, 16GB of ram, i74720HQ processor.
I have two Ubuntu VM that I have used the last time Monday (yesterday) and 2 weeks ago. Today I tried to start one of them and it returned an error. I tried the second one: the same error.
Here is the message I get:
---------------------------------------------------------------------------------------
Failed to open a session for the virtual machine Ubuntu 01.

The virtual machine 'Ubuntu 01' has terminated unexpectedly during startup with exit code 1 (0x1). More details may be available in 'C:\Users\v17ni_000\VirtualBox VMs\Ubuntu 01\Logs\VBoxHardening.log'.

Result Code: E_FAIL (0x80004005)
Component: MachineWrap
Interface: IMachine {b2547866-a0a1-4391-8b86-6952d82efaa0}
---------------------------------------------------------------------------------------

Attached are the log files.

What I tried:
- uninstall VB 5.18 and install VB 5.20 (with the relative service pack, as administrator, with antivirus disabled)
- Check that virtualization is activated, using Intel Processor Identification Utility
- Decrease the ram required by the VM
- Decrease the processors used by the VM

Can someone help me understand what went wrong ?

Thanks
JPV

[mpack]

Please read Howto: Diagnosing VirtualBox Hardening Issues.