Sometimes if you haven't cleared your browser's cache in a while the pieces start acting funny. Or it might be a bug, but a cache clear is worth trying. The restriction will go away if you play some games; not sure how many "clean" games it takes.
Game Rules Not Working
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OK, thanks I will try closing down my browser. Thanks.
Closing down your browser isn't quite what I mean. You actually have to clear your cache. Here's what you need to do in chrome; your browser may be a little different, but the principle is the same.
Obliterate the following items from: the past hourthe past daythe past weekthe last 4 weeksthe beginning of time
Browsing history
Download history
Cached images and files
Passwords
Autofill form data
Hosted app data
Hitting alt-f4 also helps clear the board.
There was a check mark next to "cached images and files" when I copied and pasted that but it disappeared. 
I use FireFox and it is pretty easy to clear various parts of the history file. But I would not want to clear it all. "Autofill" which completes entries with what you did last time would be wiped out. So I would never do a complete wipeout of the history.
If the problem is due to a polluted memory then the right solution is sutdown with restart.
I started one game as black and the white aborted. This happened 3 times. The 4th time I was made white and found that I was unable to move my pawns, so my game eventually aborted.
Now I have been put on 5 minute restrictions between games for not following the rules.
The game program is not working properly. Someone should look into this.