下面二个循环去掉任何一个都正常，二个都在就出错：a child row was mutilple parents.

Dim dt1 As DataTable = DataTables("凭证")
Dim dt2 As DataTable = DataTables("凭证明细")
Dim Customers As List(Of String)
Customers = dt1.GetUniqueValues("", "凭证类别")

With Tables("凭证")
For Each Customer As String In Customers
     Dim r As  Row = .Addnew()
     r("凭证类别") = Customer
     r("凭证ID") = "合计"
Next
End With

With Tables("凭证明细")
For Each Customer As String In Customers
     Dim r2 As  Row = .Addnew()
     r2("凭证类别") = Customer
     r2("凭证ID") = "合计"
Next
End With

看这一节的最后一段话：

http://help.foxtable.com/topics/0106.htm