Hello,
I am running VirtualBox on Windows 10. It is the latest version,
VirtualBox grafische gebruikersinterface
Versie 5.0.20 r106931
The VirtualBox itself starts correctly, but when I try to start the Ubuntu virtual machine, I get:

The VboxHardening.log says:
81c.22e4: VirtualBox.exe: timestamp 0x57220aaf (rc=VINF_SUCCESS)
81c.22e4: Error (rc=-5618):
81c.22e4: Process image name does not match the exectuable we found: \Device\HarddiskVolume4\Program Files\Oracle\VirtualBox\VirtualBox.exe vs \Device\HarddiskVolume4\PROGRA~1\Oracle\VIRTUA~1\VIRTUA~1.EXE.
81c.22e4: Error (rc=-5618):
81c.22e4: supHardenedWinVerifyProcess failed with Unknown Status -5618 (0xffffea0e): Process image name does not match the exectuable we found: \Device\HarddiskVolume4\Program Files\Oracle\VirtualBox\VirtualBox.exe vs \Device\HarddiskVolume4\PROGRA~1\Oracle\VIRTUA~1\VIRTUA~1.EXE.
81c.22e4: Error -5618 in supR3HardNtChildPurify! (enmWhat=5)
81c.22e4: supHardenedWinVerifyProcess failed with Unknown Status -5618 (0xffffea0e): Process image name does not match the exectuable we found: \Device\HarddiskVolume4\Program Files\Oracle\VirtualBox\VirtualBox.exe vs \Device\HarddiskVolume4\PROGRA~1\Oracle\VIRTUA~1\VIRTUA~1.EXE.
81c.22e4: supR3HardNtEnableThreadCreation:
This is strange, because this not referring anything of Ubuntu itsellf, it is about the VirtualBox.exe.
Yesterday, it was all working correctly, and I closed Ubuntu in a normal way.
Anyone any idea what is happening here?