Q:

Randomly getting booted off of SSH despite sending keepalives

I’ve cooked up a Debian 7 virtual machine (with VirtualBox) in an attempt to play with setting up my own server and other such cool tricks.  This is all on one computer. 
I can SSH into the virtual machine via putty, but after a short (inconsistent duration, ~15 seconds to ~3 mins) period I get booted off the server with the good 'ol error. 

Server unexpectedly closed network connection. 

Naturally, I just changed my putty settings so that I will send a keepalive every 25 seconds. 
This didn’t work, and now I'm straight out of ideas as to what to do to stop this, and I don't know if my error is somewhere in sshd_config or my putty configurations or any host of other possible things.  Spending a while on Google also hasn’t turned up anything.  
Looking through my sshd logs, my putty error logs, and my sshd_config isn't showing anything out of the ordinary. 
EDIT: Here is my putty error log:
2015-02-20 15:03:28     Looking up host "127.0.0.1"
2015-02-20 15:03:28     Connecting to 127.0.0.1 port 3022
2015-02-20 15:03:28     Server version: SSH-2.0-OpenSSH_6.0p1 Debian-4+deb7u2
2015-02-20 15:03:28     Using SSH protocol version 2
2015-02-20 15:03:28     We claim version: SSH-2.0-PuTTY_Release_0.63
2015-02-20 15:03:28     Doing Diffie-Hellman group exchange
2015-02-20 15:03:28     Doing Diffie-Hellman key exchange with hash SHA-256
2015-02-20 15:03:28     Host key fingerprint is:
2015-02-20 15:03:28     ssh-rsa 2048 ------------------------------
2015-02-20 15:03:28     Initialised AES-256 SDCTR client->server encryption
2015-02-20 15:03:28     Initialised HMAC-SHA-256 client->server MAC algorithm
2015-02-20 15:03:28     Initialised AES-256 SDCTR server->client encryption
2015-02-20 15:03:28     Initialised HMAC-SHA-256 server->client MAC algorithm
2015-02-20 15:03:32     Sent password
2015-02-20 15:03:32     Access granted
2015-02-20 15:03:32     Opening session as main channel
2015-02-20 15:03:32     Opened main channel
2015-02-20 15:03:32     Allocated pty (ospeed 38400bps, ispeed 38400bps)
2015-02-20 15:03:32     Started a shell/command
2015-02-20 15:04:56     Server unexpectedly closed network connection

EDIT x3: Here are the relevant results of an example failed session after looking at /var/log/auth.log.  
Feb 21 16:16:38 CGIT sshd[2559]: Accepted password for web from 10.0.2.2 port 60037 ssh2
Feb 21 16:16:38 CGIT sshd[2559]: pam_unix(sshd:session) session opened for user web by (uid=0)

EDIT x2:
I've reinstalled debian in a new VM instance (this time through a CD install instead of a netinstall) and yet I still get disconnected randomly.  This happens when running the VM as admin, and disabling all antivirus. 

A:

Well, the error was a problem with VirtualBox. 
https://forums.virtualbox.org/viewtopic.php?f=1&t=66067
If you have this error, you may upgrade to version 4.3.23 and your problems may be fixed.