主题：赋值报错？怎么解决

For Each rr As Row In Tables("毕业生报表").Rows
    If rr.IsNull("学号") = False Then
        If rr("学号") Like "200*" Then
            Dim lb1 As String
            lb1 = rr("学号").SubString(4,1)
            If lb1 Like "1*"
                Then rr("层次") = "本科"
            ElseIf lb1 Like "2*"
                Then rr("层次") = 专科
            ElseIf lb1 Like "3*"
                Then rr("层次") = 专科
            Else
                rr("层次") = 待查
            End If
        End If
    End If
   
Next

此主题相关图片如下：qq截图20150422023051.jpg

报错？