It happens. Sometimes it's a time lag problem when more than one person joins a game with the same person. Sometimes they don't like your opening move. Just ignore it and move on.
cheers - it happened every time before the first move. The lag between me hearing that "beep" and me returning to that window was never more than 2 seconds.
It's happened a few times today. What's that all about? It takes the fun out of playing :(