Error messages

I use javascript to edit and have popup error messages. I also use cfinput for popup error messages. However, there are some that must be submitted to the server for validation, such as ldap. I submit the payroll number on my form and this is what I do to get messages somewhat consistent.
In the action page, I query and if the payroll number is not found,
<cfif qryldap is "0">
<cflocation url="back_to_form.cfm">

I force a retur to the forms page and the output the error message :
<script language="javascript">
alert ("Payroll Number not found")>
</script>

This works ok because the error message does popup in the forms page, so it is consistent with the others.

The problem/question is when they click refresh, the error message always seems to be there and pops up all the time. How can I eliminate that from happening ? I only want it to popup once, to let them know that it is an invalid payroll number, not each time they refresh or enter the form.

Thanks