When_Validate_Record form personalization on sales Order Line Form

 I had requirement to make Customer_po_number value should be entered by user on sales order line. If not entered then it should show error message.

Please find below action:

a) "Trigger Event" to WHEN-VALIDATE-RECORD
b) "Trigger Object" to LINE
c) "Condition" to :system.current_block='LINE' and :LINE.cust_po_number IS NULL
d) "Processing Mode" to 'Only in Enter-Query Mode'

1. Click on the Actions Tab.
2. Enter a new sequence number, and set the "Type" column to 'Message' and ensure Language field is set to 'All' and this is enabled.
3. Set Message Type "Error" (without Quotes) This is the key.
4. Set Message Text "Customer PO Number is required".
5. Click the 'Apply Now' Button, and then Click on Save Icon.

To check if its working or not, First close form entirely, requery form and try to create new records and check if personalization is working