Intel VT-X is enabled in Virtualbox but it doesn't seem to pass through the needed vmx extension despite the following variables on the host confirming it is enabled:
OVF Tool: Disk progress: 99%
OVF Tool: Transfer Completed
OVF Tool: Powering on VM: Embedded-vCenter-Server-Appliance-
OVF Tool: Task p........
In plain English this happens after you upgrade VBOX and it rebuilds kernel modules based on a newer kernel than you are running (eg. you upgraded your kernel but haven't booted into it).
It is too bad there is not a standard work around that would allow it to realize this and keep old kernel modules and use them if it detects your current kernel is older than the most recently build modules.
RTR3InitEx failed with rc=-1912 (rc=-1912)