I made a new droplet today (Ubuntu 14.04 LAMP image) and I'm having some trouble with my SFTP connections. Whenever I connect via SFTP (using root) I always get disconnected after about 5 minutes of inactivity. The client becomes unresponsive for around 15 seconds and shows this error:

Network error: Software caused connection abort

This happens on both WinSCP and FileZilla with the exact same error message. I have not edited any configuration files on the droplet or installed anything else apart from phpmyadmin.

How can I stop my SFTP sessions from disconnecting so often?

Tried adding "ServerAliveInterval 60" to ssh_config and restarted the ssh service but it didn't make any difference