Form Personalization

 Not sure if this posting is in the right forum but I need help with a form personalization.  I am trying to prevent users from entering a particular distribution account on PO lines that are "expense". 

Trigger event = When-validate-record

Trigger Object = PO_DISTRIBUTIONS

Condition = :PO_DISTRIBUTIONS.CHARGE_ACCOUNT_FLEX = '0000.1990.0000.0000.0000.0'
and :PO_Distributions.Destination_type = 'Expense'

When I create a PO with this condition, I do not see my error message, even when I save the record and approve the PO.  When I validate the condition in the forms personalization screen, the condition is true.  I assume the trigger event or trigger object are incorrectly set and the personalization is being checked at the wrong time.  I cannot come up with the correct combination of settings to make this work.  Any help would be GREATLY appreciated.