Without seeing your Javascript validation routine, the onClick calling "MM_validateForm" looks like the culprit.
Try this:
Code:
<form name="MusicSelection" method="post" action="FormToEmail.php" onsubmit="return false;">
Your Javascript validation routine should submit the form after it validates and returns "true".
In the event that this doesn't work, you'd do well to post your MM_validateForm Javascript as we've no way of telling where you might have made an error.