使用ScriptControl控件时,出现"System.NullReferenceException: 这个集合中找不到此项目"错误

Question

高手帮我看看这段代码怎么了,我怎么也想不明白了
 'pStrFormula="1+2"
  Private Sub CalCulate(ByVal pFeature As IFeature, ByVal pStrFormula As String)
        Try
            Dim pResult As Double            Dim pStrSub As System.Text.StringBuilder
            pStrSub = New System.Text.StringBuilder
            pStrSub.Append("Sub CalThis()")
            pStrSub.Append(Chr(13))
            pStrSub.Append(Chr(10))
            pStrSub.Append(" pFeature.Value(pFeature.Fields.FindField(UltraLabel4.Text.Replace("" = "", """"))) = ")
            pStrSub.Append(pStrFormula)
            pStrSub.Append(Chr(13))
            pStrSub.Append(Chr(10))
            pStrSub.Append("End Sub")            AxScriptControl1.AddCode(pStrSub.ToString)
         
            AxScriptControl1.Run("CalThis()", Nothing)          Catch ex As Exception
            MsgBox(ex.ToString, MsgBoxStyle.Information, "提示")
        End Try
    End Sub