主题：[求助]报错原因？

Dim r As Integer = Tables(Km & "小题分析").Cols("难度").Index
Dim q As Integer = Tables(Km & "小题分析").Cols("区分度").Index

ElseIf Lx = "单项填空"  Then
    dr("难度") = Tables(Km & "小题分析").Aggregate(AggregateEnum.Average, 0, r, 14, r)
    dr("区分度") = Tables(Km & "小题分析").Aggregate(AggregateEnum.Average, 0, q, 14, q)   
ElseIf Lx = "完形填空"  Then
    dr("难度") = Tables(Km & "小题分析").Aggregate(AggregateEnum.Average, 15, r, 34, r)
    dr("区分度") = Tables(Km & "小题分析").Aggregate(AggregateEnum.Average, 15, q, 34, q)
ElseIf Lx = "阅读理解"  Then
    dr("难度") = Tables(Km & "小题分析").Aggregate(AggregateEnum.Average, 35, r, 54, r)
    dr("区分度") = Tables(Km & "小题分析").Aggregate(AggregateEnum.Average, 35, q, 54, q)
ElseIf Lx = "写作"  Then
    dr("难度") = Tables(Km & "小题分析").Aggregate(AggregateEnum.Average, 55, r, 56, r)
    dr("区分度") = Tables(Km & "小题分析").Aggregate(AggregateEnum.Average, 55, q, 56, q)
ElseIf Lx = Km  Then
    dr("难度") = Tables(Km & "小题分析").Aggregate(AggregateEnum.Average, 0, r, 56, r)
    dr("区分度") = Tables(Km & "小题分析").Aggregate(AggregateEnum.Average, 0, q, 56, q)
Else
End If

当代码执行ElseIf Lx = "单项填空"  Then时报错，其它“完形填空”、“阅读理解”等就没问题。是怎么回事？请指教。谢谢! 

此主题相关图片如下：报错.jpg