Cannot add constraint to DataTable 'Price' which is a child table in two nested relations

Dim Uri As Uri = New Uri(WSURL)
Dim Req As WebRequest = WebRequest.Create(Uri)
Dim send As Byte() = Encoding.Default.GetBytes(strXML)
Req.Method = "POST"
Req.ContentType = "text/xml"
Req.ContentLength = send.Length
Req.Headers.Add("Accept-Encoding", "gzip, deflate")
Dim ds As New DataSet
Dim wtr As Stream = Req.GetRequestStream
wtr.Write(send, 0, send.Length)
wtr.Flush()
wtr.Close()
Using WebResponse As HttpWebResponse = Req.GetResponse()
Dim responseStream As Stream = WebResponse.GetResponseStream()
If (WebResponse.ContentEncoding.ToLower().Contains("gzip")) Then
responseStream = New GZipStream(responseStream, CompressionMode.Decompress)
ElseIf (WebResponse.ContentEncoding.ToLower().Contains("deflate")) Then
responseStream = New DeflateStream(responseStream, Comp ...