encountered this when booting a 64 bit edition iso :
VT-x/AMD-V hardware acceleration has been enabled, but is not operational. Your 64-bit guest will fail to detect a 64-bit CPU and will not be able to boot.
Please ensure that you have enabled VT-x/AMD-V properly in the BIOS of your host computer.
I thought a reboot would load all required kernel modules , but I rebooted primarily to get into BIOS which I could not in first attempt .
No a reboot didn't help , hence went this time patiently to the BIOS and enabled the intel virtualisation support and hurray it worked !
Networking: The default NAT mode is suitable for basic usage like : ping outside and connect to internet . But I wanted to ping from my machine to VM which I couldn't do with the NAT mode . Hence I had to go for bridged mode .
For which I installed bridge-utils package and configured my /etc/network/interfaces to add bridge entries . Then in my VM config I changed it to bridge where I selected the bridge device br0 . Now both real and virtual machines have Ip addresses !
The rest was plain simple .. everything was matter of clicks , things did come a long way !!