Same thing happened to me with error code 318, Spoke to Cutomer Support but no satisfactory answer I got from them.
I figure out why this happen to me. Sometimes my internet connection drops and came back very fast and ESO server receive information from my PC multiple time within a time period and their server firewall recognise these info as spam, So firewall kicked me from server. When this happen again to u, just quit game and try to measure ur speed and ping.