VirtualBox cannot establish session to virtual PC

I can't run my Virtual OS in VirtualBox. I Use Windows 10. I have Hyper-V disabled.
The error dialog:

VMMR0_DO_NEM_INIT_VM failed: VERR_NEM_MISSING_KERNEL_API_2 (VERR_NEM_MISSING_KERNEL_API_2).
VT-x is not available (VERR_VMX_NO_VMX).


Return code: 
E_FAIL (0x80004005)
Component: 
ConsoleWrap
Interface: 
IConsole {872da645-4a9b-1727-bee2-5585105b9eed}

any idea, what's wrong ? Thanks.