I have had the same problem from time to time. I thought it was because I was playing on two computers at different times, but it just seems random. I posted on the troubleshooting thread, and the only advice was:
1. Reboot
2. Try it on other computers
3. Try it on other browsers
4. Wait and it goes away
The only thing that worked for me was 4. I still can't play T50 maybe half the time. Shrug.
C