Linq nullReferenceException problem

Replace your Selects with Lets:

Dim strURLSearch As String

        strURLSearch = "http://isbndb.com/api/books.xml"

        strURLSearch = strURLSearch & "?access_key=CYGCL3GT"

        strURLSearch = strURLSearch & "&index1=isbn&value1=" & Me.txtISBN.Text

        Dim xResults As XElement = XElement.Load(strURLSearch)

        Dim books = From BookData In xResults.Descendants("BookData") Let Title = BookData.Element("TitleLong").Value Let Author = BookData.Element("AuthorsText").Value Let Publisher = BookData.Element("PublisherText").Value

        For Each BookData In books

            Me.txtResults.Text = Me.txtResults.Text & BookData.Author & vbCrLf

        Next