If it happens again, click on your opponent's last move (in the move list on the game-chat screen) then you should be able to move.
If this does not work or there was some other problem, please send us the game:
1. Click on your avatar, then "My Games";
2. Click into the game with the where you had problems moving;
3. Click on the Send Game to a Friend button;
4. Add email@example.com as the email address to send to;
5. Describe what happened, including move number in the message section;
6. Click on Send.
Feel free to discuss any bugs, comments or suggestions in this thread. All content will be monitored by the Community and Moderators.