主题：合并统计出现的错误提示，如何解决？

Dim bd1 As New GroupTableBuilder("统计表1",DataTables("OutDtl"))
Dim dt1 As fxDataSource
bd1.Groups.AddDef("ItcNam")
bd1.Groups.AddDef("DocTm", DateGroupEnum.Year, "Yr")
bd1.Groups.AddDef("DocTm", DateGroupEnum.Month,"Mn")
bd1.Groups.AddDef("DocTm", DateGroupEnum.Day, "Dt")
bd1.Totals.AddDef("Amn", "AddAmn")
dt1 = bd1.BuildDataSource()

Dim bd2 As New GroupTableBuilder("统计表2",DataTables("AcpDtl"))
Dim dt2 As fxDataSource
bd2.Groups.AddDef("ItcNam")
bd2.Groups.AddDef("DocTm", DateGroupEnum.Year, "Yr")
bd2.Groups.AddDef("DocTm",DateGroupEnum.Month,"Mn")
bd2.Groups.AddDef("DocTm", DateGroupEnum.Day, "Dt")
bd2.Totals.AddDef("Amn", "RdcAmn")
bd2.Filter = "[WayID] = 'MG'"
dt2 = bd2.BuildDataSource()

Dim cls = "ItcNam,Yr,Mn,Dt"

dt1.Combine(cls,dt2,cls)

Tables("AcpAcc_Table1").DataSource = dt1

以上会报错，删除关于日期的分组就不会报错？这是为什么？如何解决？