主题：[求助]赋值报错

Dim nian As WinForm.ComboBox = e.Form.Controls("ComboBox1")
Dim yue As WinForm.ComboBox = e.Form.Controls("ComboBox2")
If  nian.Value  Is Nothing Then
MessageBox.Show("请选择年份")
ElseIf  yue.Value  Is Nothing Then
MessageBox.Show("请选择月份")
End If
For Each sj As DataRow In DataTables("工资表").DataRows
  If sj.IsNull("姓名")=False
 dr("工资月份") =  nian.Value & "年" & yue.Value & "月"
End If
Next

这段代码的赋值怎么老报错呢？究竟赋值用什么格式呢？