The first step is to check to see if the PaperCut NG/MF is listening on the port. The command:
netstat -anp | grep 9191
should list the pc-app as the owner of the process on port 9191. If nothing is listed, check that the has started (e.g. ps -ef | grep pc-app).
If the server is already running, the next step is to ensure no IP filtering is applied to the port. Some Linux distributions have strict iptables enabled by default. Ensure that port 9191 is accessible from all local network systems.