Generally the message means that the kernel popped a cork and tried to dump core to the swap partition, which is too small to contain the data. Most likely there is a less trivial root cause that causes it to pop a cork in the first place.
Unless the system dumpdev and dumpdir are override, normally a swap partition should be no smaller then the physical memory, other wise it is impossible to get a core dump from the kernel.
You can turn off core dumps by booting off the install CD: after setting up the language/keyboard layout, right click on the background and hit 'xterm' in the menu that comes up. Locate your hard drive numbering, either in the installer or /dev. Mount your bsd partition(s) and append dumpdev="NO" to your etc/rc.conf or etc/rc.conf.local file on the partition.
example# echo 'dumpdev="NO"' >> /mnt/etc/rc.conf.local
When done, umount the partition(s) and reboot. Test if the system still crashes.
Also note that when using software such as VirtualBox, VMWare, VirtualPC, and the like -- you are not testing on the live hardware but on virtual hardware emulated by software running on the live hardware, so YMMV when shifting from a virtual pc to a live pc!