This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
<tr> is representing a row of the particular table.. Here if you want to have data inside the row you must enclose it with <td> or <th> if it is your header.
You have <table> inside the <tr> but no <td> or <th>, so it complains