Have you tried uninstalling the game and deleting the Pox Nora folder from your install directory? It could be a file became corrupted otherwise it is possible that one of your computer's settings was changed. Try going through the Troubleshooting list. http://forums.poxnora.com/index.php?threads/pc-troubleshooting.1487/
Are you using a VPN? This is a connection problem and could be caused by a information desync. You might want to check your firewall and security settings. Also, are you using the Steam or standalone version form PoxNora.com?
Definitely not using a VPN. Using the standalone version from PoxNora.com. What changes do you want me to make to my security and firewall to prevent this? The various places I usually encounter errors are: Unable to connect to poxnora.com. Please check your local connection, and try again later. (The client updater) General error. Unable to login. NullPointerException. (Login window) Unable to connect to poxnora.com. Please check your local connection, and try again later. (Login window)
That is where this get's tricky because any number of things can cause this. Your malware/antivirus/internet security software could be causing this. Your firewall restrictions could be too high. You could have a virus that is causing this or an out of date driver. The best thing to do is go through our Troubleshooting tips. http://forums.poxnora.com/index.php?threads/pc-troubleshooting.1487/ But you might also want to try the Steam version of Pox Nora too. Not knowing what is causing the this issue some times just running Steam bypasses the issues. But make sure all your drivers are up to date.