How to display custom error message in post notification function

Hi,

We are building a workflow where we need to raise a custom error message (You cannot reassign this notification to the preparer of this batch) whenever the approver reassigns the notification to certain user. We can able to raise standard predefined error through API WF_CORE.TOKEN and WF_CORE.RAISE. But it displays only the messages present in the table WF_RESOURCE. We need to raise a custom message instead of the above.

Please let us know how to achieve this.

Thanks,

Krushna