Set user defined item to invisible

Hi all.

I want to set user defined item to invisible but it doesn't work.Here is my code:

Dim form As SAPbouiCOM.Form

Dim sFormType As String

Dim formCount As Integer

Dim sboUDFform As SAPbouiCOM.Form

If (pVal.FormTypeEx = "-940") And pVal.BeforeAction = True Then

If pVal.EventType = SAPbouiCOM.BoEventTypes.et_FORM_LOAD Then

form = SBOApplication.Forms.Item(pVal.FormUID)

sFormType = "-940"

formCount = 1

sboUDFform = SBOApplication.Forms.GetForm(sFormType, formCount)

sboUDFform.Items.Item("U_Dimension1").Visible = False 'Set ComboBox Item to invisible

End If

End If

Anyone can help me.Thanks