before you can try to resolve it, you need to figure our what the problem is.
The error tells you that Output file repository server is down.
Is it down when this error happens ?
Does OFRS crashes (its PID changes during this time ?) ?
Do you have OFRS logs from the time you get error ?
Firewall shouldn't be a problem since it works most of the time, if it was a firewall issue - it'll fail all the time and not just connecting to OFRS.