是什么导致我的 SSRS 图表中出现范围参数错误?

What is causing a scope parameter error in my SSRS chart?

为什么我的图表会出现这个错误? (Chart Image)

我在图表中使用了这个表达式:

Series:

=Sum(Fields!Mins_Att.Value)/Sum(Fields!Mins_Poss.Value)

Series 1: 

=Sum(Fields!Mins_Att.Value, 
         "Chart2_CategoryGroup2")/Sum(Fields!Mins_Poss.Value, "Chart2_CategoryGroup2")

我收到这个错误:

The Y expression for the Chart has a scope parameter that is not valid for an aggregate function. The scope parameter must be set to a string constant that is equal the name of group, data region or name of dataset.

报告中不存在 "Chart2_CategoryGroup2" 的范围。