Updating the Price for a PO Line ... What's Wrong?

Question

Both MsgBoxes return the correct values.  So, the B1 Purchase Order object appears to be functioning correctly.  However, the POR1 table is not updated in the database.  What am I doing wrong?
Dim oPO As SAPbobsCOM.Documents
Dim oPO_Lines As SAPbobsCOM.Document_Lines
oPO = oCompany.GetBusinessObject(SAPbobsCOM.BoObjectTypes.oPurchaseOrders)
oPO.GetByKey(lBaseRef)
oPO_Lines = oPO.Lines
oPO_Lines.SetCurrentLine(lBaseLine)
MsgBox("Before Update: Price = " & oPO_Lines.Price)
oPO_Lines.Price = dPrice
MsgBox("After Update: Price = " & oPO_Lines.Price)
oPO.Update()
oPO.Close()
lBaseRef and lBaseLine were assigned from a Purchase Invoice before this code was executed.

Answer 1

Ah!  I figured this out.  The Purchase Order is Closed (and unedittable at the database level) once the Purchase Invoice is created for these items.  Therefore, the assignement of dPrice to the Price column is "NOT" updated in the POR1 table.
Too bad that exceptions are not raised for such errors.  Also, it is confusing that the 2nd MsgBox() shows a misleading "updated" value.  Apparently, data validation is being handled at two layers in the application.  Why?  I would assume SAP would implement the validation at the business logic layer, especially given the recommendations to develop all customizations through the SDK.
I can perform the update using a recordset query; but, this direct editting of the table would require modifying several lines in both the POR1 and OPOR tables.  Thus, this solution (my only solution for this project) would be extraordinarily difficult to maintain.  Therefore, I am going to recommend dropping this implementation requirement.