This constraint cannot be enabled as not all values have corresponding parent values in c#?

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C#

.NET

WinForms

Gridview

I tried to populate data's in nested gridview. Am getting this error This constraint cannot be enabled as not all values have corresponding parent values. What is my error ? Help me to solve this.

This is my code

validateDept.InitializeConnection();
        OleDbConnection connection = new OleDbConnection(validateDept.connetionString);

        OleDbDataAdapter AdapterCustomers = new OleDbDataAdapter(
         "SELECT EmployeeId, FirstName FROM Employee", connection);
        OleDbDataAdapter AdapterInvoices = new OleDbDataAdapter(
          "SELECT InvoiceId, InvoiceNumber, InvoiceDate, SalesPerson AS EmployeeId, Customername AS CustomerId, (Select CustomerName from Customer where Customer.CustomerId = NewInvoice_1.CustomerName) AS Customer_Name, DueDate, Tax, GrandTotal, CompanyId, InvoiceStatus FROM NewInvoice_1", connection);

        DataSet dataSet11 = new DataSet();
        //Create DataTable objects for representing database's tables
        AdapterCustomers.Fill(dataSet11, "Employee");
        AdapterInvoices.Fill(dataSet11, "Invoices");

        //Set up a master-detail relationship between the DataTables
        DataColumn keyColumn = dataSet11.Tables["Employee"].Columns["EmployeeId"];
        DataColumn foreignKeyColumn = dataSet11.Tables["Invoices"].Columns["EmployeeId"];
        dataSet11.Relations.Add("CustomerInvoice", keyColumn, foreignKeyColumn); // Getting error on this row

        //Bind the grid control to the data source
        gridControl1.DataSource = dataSet11.Tables["Employee"];
        gridControl1.ForceInitialize();

        //Assign a CardView to the relationship
        GridView cardView1 = new GridView(gridControl1);
        gridControl1.LevelTree.Nodes.Add("CustomerInvoice", cardView1);
        //Specify text to be displayed within detail tabs.
        cardView1.ViewCaption = "Invoice List of a Customer";

        //Create columns for the detail pattern View
        cardView1.PopulateColumns(dataSet11.Tables["Invoices"]);

Thnakyou,
Srihari