On the Windows 10 April 2018 (1803) host go to Windows Defender Security Centre > Device Security > Core Isolation and disabled the settings there?
Thanks for your reply. Will try it later and let you know if that will work.
For me, there's only one option "Memory integrity" and it is off already.
Any other advice?
Is Hyper-V also disabled?
What is the exact error message you are getting when you try to start a VM?
This odd Windows 10 behaviour of reporting that Hyper-V is installed when it appears not to be in Turn Windows features on and off has been reported in other places.
From Microsoft's TechNet forum a post had this to say about Device Guard and Credential Guard and the Hyper-V problem:
Credential guard is the root of the problem. Thanks for the post!
I was able to disable credential guard by using microsoft's Device Guard and Credential Guard hardware readiness tool: https://www.microsoft.com/en-us/download/details.aspx?id=53337
First, make sure it isn't managed by group policy. Check local group policy for the following and disable:
Computer configuration > Administrative Templates > System > Device Guard > Turn on Virtualization Based Security: disabled
The tool is a powershell script so make sure to set your powershell exexution policy:
Set-ExecutionPolicy -ExecutionPolicy RemoteSigned
Then run the readiness tool with the disable flag:
When you reboot you should get a preboot dialougue asking if you want to disable credential manager
I would also make sure to have hyper-v disabled in windows features.
Disable-WindowsOptionalFeature -Online -FeatureName Microsoft-Hyper-V –All
You may also need to disable it from starting by using a command line command mentioned before:
bcdedit /set hypervisorlaunchtype off
There is also reference to the VMware KB:
If you want to read the full thread it is available here.