both of these worked for me:
Code:
<html>
<head>
<script language="JavaScript">
function validateProd() {
   if(document.getElementById('sname1').value == '') {
      alert('Your name is a required field. Please try again.');
      return false;
   }
   if(document.getElementById('scode1').value == '') {
      alert('Your name is a required field. Please try again.');
      return false;
   }
   if(document.getElementById('Docket1').value == '') {
      alert('Your name is a required field. Please try again.');
      return false;
   }
   return true;
}
</script>
</head>
<body>
<br />
<form method="POST" name="addImage" id="addImage" action="index2.php" onSubmit="return validateProd();">
<input type="text" name="sname1" id="sname1" size="10">
<input type="text" name="scode1" id="scode1" size="10">
<select name="Docket1" id="Docket1"><option value=""></option><option value="A">A</option></select>
<input type="submit" value="submit">
</form>
</body>
</html>
Code:
<html>
<head>
<script language="JavaScript">
function validateProd() {
   if(document.addImage.sname1.value == '') {
      alert('Your name is a required field. Please try again.');
      return false;
   }
   if(document.addImage.scode1.value == '') {
      alert('Your name is a required field. Please try again.');
      return false;
   }
   if(document.addImage.Docket1.value == '') {
      alert('Your name is a required field. Please try again.');
      return false;
   }
   return true;
}
</script>
</head>
<body>
<br />
<form method="POST" name="addImage" id="addImage" action="index2.php" onSubmit="return validateProd();">
<input type="text" name="sname1" id="sname1" size="10">
<input type="text" name="scode1" id="scode1" size="10">
<select name="Docket1" id="Docket1"><option value=""></option><option value="A">A</option></select>
<input type="submit" value="submit">
</form>
</body>
</html>
Does your browser have a javascript console? Perhaps it's throwing some errors that might be helpful. Hope this helps.