Error Message in event viewer
Failed to connect to servername.domain.com:13391 Failed to initialize session with document engine: Unable to resolve Contentdistributor.
I got this error log several times. One is from Office Web Apps installation.
I installed FAST for SharePoint before deploying OWA. after that i got this error.
the other one I think it occurs after FAST and SharePoint Server were migrated to a new server using vMotion.
Just reinstall FAST Certificate into SharePoint Server again follow the step in the below link.
Configure SSL enabled communication
then restart both FAST and SharePoint server.