This is actually what's causing a lot of people here to have problems. Whether intentional on their part or completely circumstantial, if you're somehow deleting cookies for rpgcodex.net (or not whitelisting this site) then the server can't remember who you are and thus triggers a fresh 2FA authentication.Maybe he hears voices telling him to delete cookies often.
If you use programs like McAfee Security or Norton 360 or even something like CCleaner, these can all potentially delete that cookie that 2FA is looking for when you log in. Exclude RPG Codex from that cleanup list and it might solve your problem.