You can launch wireshark on the background to capture your trafic, then you can find out more info... like your ISP issue(Speed) or need to finetune your TCP/IP setting on your PC.
Check the latency between your PC and the game server as well...
Basic guide to wireshark --> w_w_w.howtogeek.com/104278/how-to-use-wireshark-to-capture-filter-and-inspect-packets/
GW2 Wiki doesn't show exact error code as 58:11:504.101...
I say open a ticket to tech support... OR... do you know someone else has a laptop to try GW2 @ your home?
see If you can duplicate the same error on other PC/laptop...