Remote debugging loses settings (and fails)

I have been using remote debugging on a complex project for several months. I go to remote debug today and the IDE will not connect. Clicking cancel provides a box that wants to add host '' to known hosts (with a relevant fingerprint). Just waiting leaves a progress bar that churns forever. I added extended debugging and see that the IDE is using the correct host ip and user id. A snippet of the log is attached.

'    <category name="#com.jetbrains.plugins.webDeployment">
        <priority value="DEBUG"/>
     </category>
' was added to xml.log

I have tried:
  clearing cache and restarting
  removing all remote debuggers and recreating them
  setting up remote debugging to a different host

Is there anyway to clear the known systems that PyCharm is using? Somewhere in the configuration it is confused.

Running on Ubuntu 14.04
Connecting to system running Debian Wheezy
Python 2.7
PyCharm 3.4.1