I have VB hosting Ubuntu running on two machines. When on one, all worked fine. I added it to my notebook and then neither machine could use Win network shares that had previously been created. All other machines could reach either without problem.
Ping from both machines showed the others IP at xxx.xxx.xxx.54. Network access from the other machine and Remote Console both fail.
I finally fixed this by changing the VirtualBox Host Only Adapter to use dynamic addresses.
Scott