A couple of things to look at:
- Webserver logs. See if there is information in the webserver logs when the error happens. If nothing is showing up, increase the debug level to get more diagnostic information.
- Use a packet capture utility like Wireshark to capture data at both the client and the server ends. This may capture some of the conversation that the logs may not.
- This could be some type of firewall issue. Take a look at the firewall logs to see if anything is being blocked when connecting to the webserver from outside of the network.
Might want to give a look here, where there’s a similar problem reported.
If not, please give some firther information on your installation.