Cannot access Ubuntu instance on Windows 7 host after ugrade

[Slowjoe]

Hi. First post.

I'm currently running a pair of Ubuntu 12.04 instances on Windows 7. The Virtualbox revision is 4.2.6 r82870. At the current time, this appears to be the latest release.

Because I spend a significant time on the train each day, I have a slightly unusual setup: three interfaces each:
1. Bridged adaptor
2. Internal network adaptor
3. Host-only adaptor

eth0 is for network access to the outside world
eth1 is for access between virtual hosts
eth2 is for access when away from a DHCP server + the convenience of WIFI.

Anyway, this was all working nicely, and then I made a pair of changes:
1. I upgraded Virtualbox. The previous version dated from the second half of last year, but I don't have the revision number.
2. I enabled 64 bit emulation in the BIOS.

The next time I attempted to ssh into the virtual hosts, I was unable to access the host-only adaptor. The following is the ping

[user@host] → ping 192.168.56.101

Pinging 192.168.56.101 with 32 bytes of data:
PING: transmit failed. General failure.
PING: transmit failed. General failure.
PING: transmit failed. General failure.

[2013-02-26 19:33.06] ~
[user@host] → ssh kbarry@192.168.56.101
ssh: connect to host 192.168.56.101 port 22: Connection timed out

I searched the forum last Friday, and didn't find an answer, so I hope I'm not doing anything terminally foolish!

[Perryg]

Type VBoxManage list hostonlyifs in a command window and see if it still exists. Sometimes on upgrades it disappears.
You can recreate it with VBoxManage (see manual) or use the preferences section -> network from the VBox main manager.

[Slowjoe]

Thanks for the response.

What worked for me in the end was to do the following:
1. remove VirtualBox
2. Switch off 64 bit emulation
3. Reinstall VirtualBox (same revision)
4. Test networking -> worked
5. Switch back on 64 bit emulation
6. Test networking -> worked

I don't know why, but I'm mentioning this in case someone else runs into the same problem.