I ran into this exact same issue and it had me scratching my head for days. I even tried an Ubuntu image, just to see if it was Centos. It wasn't Centos.
After I read through a few other forums, I finally figured out that Hyper-V still had some active components, even after I disabled the feature from Programs and Features and rebooted my computer. What really tipped me off was when I read through the vbox.log file as suggested by scottgus1
scottgus1 wrote:Look for these lines in the guest vbox.log:
{timestamp} HM: HMR3Init: Attempting fall back to NEM: VT-x is not available
{timestamp} NEM: WHvCapabilityCodeHypervisorPresent is TRUE, so this might work...
When I did this, I noticed that I had the exact same errors in the log.
Here's what I did to figure out that Hyper-V was still running:
1. Open System Information. On my Windows 10 host, the application was located under C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Administrative Tools.
2. From the System Summary tab scroll down to the bottom of the pane on the right.
If Hyper-V is not enabled what you should see should look like this:

- HyperV_Disabled.png (5.64 KiB) Viewed 686 times
If Hyper-V is enabled, you will see a message stating "a hypervisor has been detected. features required for hyper-v will not be displayed"
In order to completely disable Hyper-V after disabling it from the features list, I still had to do the following:
1. Go into Services.msc, right click on each service associated with Hyper-V, select Properties, and set the Startup Ttype: to "Disabled".
2. I had to disable the Hyper-V network adapter under Control Panel\Network and Internet\Network Connections. The adapter in my case was labeled "vEthernet (Default Swtich)"
3. I then had to reboot my computer.
After that, I was in business. I hope this helps!