Error with dropdownlist: There can not be multiple items selected in DropDownList

This error just came up in my GridView because I have 6 dropdownlist in the GridView in EditItemTemplate, and when I click Edit, this error occurs:

  

System.Web.HttpException: There can be multiple items   selected in DropDownList.

This is my Code-Behind:

 Protected Sub GridView1_RowDataBound(sender As Object, e As GridViewRowEventArgs)
    If e.Row.RowType = DataControlRowType.DataRow AndAlso GridView1.EditIndex = e.Row.RowIndex Then
        Dim ddlParIDF As DropDownList = DirectCast(e.Row.FindControl("ddlParIDF"), DropDownList)
        Dim ddlFilaIDF As DropDownList = DirectCast(e.Row.FindControl("ddlFilaIDF"), DropDownList)
        Dim ddlTabIDF As DropDownList = DirectCast(e.Row.FindControl("ddlTabIDF"), DropDownList)
        ddlParIDF.Items.FindByValue(TryCast(e.Row.FindControl("lblParIDF"), Label).Text).Selected = True
        ddlFilaIDF.Items.FindByValue(TryCast(e.Row.FindControl("lblFilaIDF"), Label).Text).Selected = True
        ddlTabIDF.Items.FindByValue(TryCast(e.Row.FindControl("lblTabIDF"), Label).Text).Selected = True

        Dim ddlFilaMDF As DropDownList = DirectCast(e.Row.FindControl("ddlFilaMDF"), DropDownList)
        Dim ddlTabMDF As DropDownList = DirectCast(e.Row.FindControl("ddlTabMDF"), DropDownList)
        Dim ddlParMDF As DropDownList = DirectCast(e.Row.FindControl("ddlParMDF"), DropDownList)
        ddlFilaMDF.Items.FindByValue(TryCast(e.Row.FindControl("lblFilaMDF"), Label).Text).Selected = True
        ddlTabIDF.Items.FindByValue(TryCast(e.Row.FindControl("lblTabMDF"), Label).Text).Selected = True
        ddlParMDF.Items.FindByValue(TryCast(e.Row.FindControl("lblParMDF"), Label).Text).Selected = True
    End If
End Sub

I use a Label inside EditItemTemplate next to the DropDownList to save the last selected value of the dropdownlist, but I realize that if I remove the ".Selected = True" from two or more Label, this error no longer happens, but the disadvantage is that it will not save the last value chosen from the DropDownList.

To fill the DropDownList I use the ListItems within the gridview.

Or if someone knows that there is another way to maintain the selected value, if you could help me too.

Thanks to everyone!