Considering e.g. the 404 you are getting I'm not sure if I would read too much into the TCP RST (the yellow on red). As IP Overview mentions under "Resetting a Connection", TCP RSTs are used to quickly tear down a connection. A 404 error on the remote side might translate into a a quick teardown scenario. The fact that the RST was also flagged with an ACK supports that.

What was the remote site? Do you recognize it? Is it a proxy or firewall? It could very well be the culprit. If not, then do the packets leading up to the TCP RST offer any clues? It's hard to troubleshoot without seeing more details (and I am by no means a network guru).