What we tried so far:
"Analyze Install for Issues" With PSO2 Tweaker
"Check for Deleted/Empty Files" With PSO2 Tweaker
"Check for Old/Missing Files" With PSO2 Tweaker
"Fixe Gameguard Errors" With PSO2 Tweaker
"Fix PSO2 EXEs" With PSO2 Tweaker
Deactivate Antivirus/Firewall
"ipconfig /flushdns" in CMD
Restart Modem/Router
Tried to login with PSO2Proxy (CyberKitsune's)