There are few reasons behind this error. Le's discuss these.
Check VT-X is enabled in the BIOS settings or not. If not than enable it.
Check if Hyper-V virtualization is enabled in Windows. This is the most common cause why this error occurs. Since .Microsoft’s Hyper-V technology is known to conflict with VT-X, the OS will automatically disable VT-x if Hyper-V virtualization is enabled. To disable this use the bellow command from Windows PowerShell.
dism.exe /Online /Disable-Feature:Microsoft-Hyper-V
Hope these steps will solve the error.