Question

Not sure why it won’t validate it’s pretty simple… any ideas?

http://pastebin.com/uMPUzH09

Answer 1

The W3 validator is pretty verbose:

Line 19, Column 7: end tag for "div" omitted, but OMITTAG NO was specified
</body>

You may have neglected to close an element, or perhaps you meant to "self-close" an element, that is, ending it with "/>" instead of ">".

You’re missing a closing </div> tag:

<div id="main_container">
    <div id="top_gray"></div>
    <div id="header">
    <div id="left_container"></div>
    <div id="center_container"></div>
    <div id="right_container"></div>
    <div id="footer"></div>
  </div>
  ^^^^^^ You forgot me
</div>