change the checkbox code:
<input name="Has_read_and_understands_disclaimer" type="checkbox" class="formCheckboxField_Standard" id="Has_read_and_understands_disclaimer" tabindex="16" value="Yes" <?php if (!(strcmp((isset($_GET["invalid"])?ValidatedField("ContactUs","Has_read_and_understands_disclaimer"):""),""))) {echo "checked=\"checked\"";} ?> />
to:
<input name="Has_read_and_understands_disclaimer" type="checkbox" class="formCheckboxField_Standard" id="Has_read_and_understands_disclaimer" tabindex="16" value="Yes" />