It means the action you are validating against on the server side with the check action method isn't in the list of valid actions you have defined for the game state
In your states.inc.php file, make sure the action is part of "possibleactions" and that it is written EXACTLY the same. You might want to make sure only the active player can select an item if the type of your state is activeplayer.
If you want further help, post your code for your selection, as well as the state part from your states.inc.php. It would be easier to pinpoint the problem.