He doesn't like the name of the function - change it to another name, eg. changeOptions, and use that. Here is a version of your code that works for me:
<html>
<body>
<script> function changeOptions(){ alert("asdfasdf"); }</script>
<select type="selectbox" name="crPaymentOption" id="crPaymentOption" onchange="changeOptions()" />
<option selected="" value="--">--</option>
<option value="Check">Check</option>
<option value="Credit Card">Credit Card</option>
<option value="Cash">Cash</option>
</select>
</body>
</html>
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