So I copied a Windows XP / 64 bit guest OS *vmd that was used by a VMWare to be used with my VirtualBox on the Ubuntu 11.10 / 64 bit host. When configured the VM to be "Windows XP", and pointed to the *vmd, when I start the guest windows operating system, the below error was printed in blue screen!
"Windows could not start because of a general computer hardware configuration problem. Attempting to load an x64 operating system, however this system does not have the APIC configured. Check your firmware settings. Make sure that the firmware has enabled the advanced programmable interrupt controller (APIC) on this system. If the firmware does not have an APIC setting, please contact the system manufacturer for a firmware update to enable the local APIC."
It took me some time to identify the root cause! VirtualBox had an option, "Windows XP / 64 bit". I should have picked that, instead of "Windows XP".
After changing this too, however, "the machine didn't close properly last time" was being thrown always, not letting the windows to start properly - even after multiple trials. For some reason, when I opened it in VMWare, it had an option, whether the image was moved or copied. When I mentioned it was moved, it started with the repair mode. After that the same *.vmd started working fine with both VMWare and VirtualBox without any issues. This was a strange issue - however, glad VMWare was able to open and fix the issue, where now I can use it with VirtualBox. For me, it seems VirtualBox eats lesser memory than VMWare.