If you use some third party anti-virus, might be a good idea to check if that has blocked anything.
One I'm still using for whatever reason, it tried to block pso2startup.exe cause it thought it was some virus. To be exact this happened when I tried opening the game/client after initial download was done(11GB~). Though it didn't seem to try stop anything straight away since it still opened/started.
(thats what it tried to "quarantine"/block)
Though still downloading rest of game files from game client, so dunno if I'm out of weird issue woods yet. >.> (seems to be using most of my DL speed, and ye, thanks for not giving option to limit its DL speed...)