Thank you, I'd read that thread and the guide on setting everything up before I'd posted. None of that post was able to get me past this issue, though.

I've gone through the nine pages again and re-did everything from scratch thinking maybe I'd missed a step. I've even disabled Windows Firewall, AVG Virus protection (since at one point it saw it as a threat), and made sure I didn't somehow reinstall Nvidia's firewall. I've tried using all three methods of logging in. I can log into either account separately and play indefinitely.

Also, for some reason, although I get the FPS meter and other info, the CTRL+SHIFT+ALT+G command when in game does nothing.