I had this problem in upgrading before, and the same solution worked: delete the virtual machine and start again (keeping the same virtual disk, of course). I think the only change I make when I do this is to the .xml file.
Attached is the new, working one, and the old one which does causes the virtual machine to crash on suspend. Perhaps it gives a clue to the problem.
Debian.xml
Description: XML document
Debian.xml_old
Description: XML document
