What client are you using? This issue is not tracked yet.
I'm playing in a web browser (Chromium) and I still keep seeing this pop-up window with error message every time I go to the site. As I said earlier, it's not a big deal because I'm always there a second later, and the site is working perfectly for me. I have already played some cash games and participated in more than 20 tournaments and have never had any issues whatsoever.