In server validations use copy and paste this as the value to be validated:
<?php echo($Recordset1->TotalRows); ?>
Choose "number" validation and click the plus button.
Then set the number validation to be greater than zero.
From there you should be able to use the concepts of this tutorial: http://www.webassist.com/tutorials/Add-server-validation-to-your-web-forms
That will allow you to add the server validation message when the check fails.