the insert record code is looking for a form element named "GrBirthDate" but there is not a form element with that name.
the date picker element is named "BirthdayPicker"
change:
<td nowrap="nowrap" align="right">GrBirthDate:</td>
<td><input id="datepicker_1" name="BirthdayPicker" type="text" value=''/></td>
to:
change:
<td nowrap="nowrap" align="right">GrBirthDate:</td>
<td><input id="datepicker_1" name="GrBirthDate" type="text" value=""/></td>