cfmessagebox error whatever parameters

Whatever parameters are used in the CfmessageBox,

I get that error :

buttonType attribute is valid only for messagebox type "confirm".

Running CF9.0

Example code:

<cfmessagebox name="PopMessage"
  callbackhandler="GrabUserInput"
  labelok="Check info"
  title="Warning!"
  icon="warning"
  type="alert"
  message="This is a message box"/>

<script type="text/javascript">
  ColdFusion.MessageBox.show('PopMessage');
</script>

Thanks for help.