object reference....

Hi To All,

In my screen there is textbox with link button. when i click the link button another screen should open... Here is my source

 Case "lnkWNo"
                        Select Case pVal.EventType
                            Case SAPbouiCOM.BoEventTypes.et_ITEM_PRESSED
                                objXML.LoadForm("aaa.xml")
                                objForm = App.Forms.Item("AAA")
                                objForm.Mode = SAPbouiCOM.BoFormMode.fm_FIND_MODE
                                objForm.Items.Item("txtOrderNo").Enabled = True
                                objForm.Items.Item("txtOrderNo").Specific.value = Datasource.GetValue("U_worderno", Datasource.Offset).Trim
                                objForm.Items.Item("1").Click()
                        End Select

When i crossed this line

      objForm.Mode = SAPbouiCOM.BoFormMode.fm_FIND_MODE

error message as

object reference not set to an instance of object

same as when i crossed this line

       objForm.Items.Item("txtOrderNo").Specific.value = Datasource.GetValue("U_worderno", Datasource.Offset).Trim
             

error message comes as

object reference not set to an instance of object

Wats the problem.........