JavaScript : Uncaught ReferenceError

ok, so when we put the folowing into the top of moodle LMS on theplayer.php page:

                    <script type="text/Javascript">

                       function myFunction(){

                               alert('Hello world");

                       }

                     </script>

and we setup a button to fire this script :

"myFunction();"

we get an error :

Uncaught ReferenceError: myFunction is not defined

is there something that we are doing wrong here ? all the tutorials that we have read says we should be able to do this quite simply with capivate 6.

its on a webserver(dreamhost) and still not working.