When browsing the Internet you see the error:
In a packet capture, you see a 503 error returned by the proxy to the client.
There are several reasons why you may see the "Network Error (tcp_error)" message:
If the problem occurs with a specific URL or destination, it may be due to one of the following:
When this problem occurs, obtain a packet capture; it is very important to see what is happening on the wire. To take a packet capture from the proxy, go to https://<IP.address.of.ProxySG>:8082/PCAP/statistics.
Download Wireshark to view a packet capture taken from ProxySG.