On the very page I am writing this post, clicking the Preview button results in a bar that says "Fetching preview..." and never shows the actual preview.
I investigated using Firefox's inspector, and the AJAX response coming back from the server is as follows (HTTP 200 status code):
<div>
<table border="0" width="80%" cellspacing="0" align="center" cellpadding="4" class="tborder">
<tr class="titlebg">
<td>An Error Has Occurred!</td>
</tr>
<tr class="windowbg">
<td style="padding: 3ex;">
Your session timed out while posting. Please go back and try again.
</td>
</tr>
</table>
</div>
<div align="center" style="margin-top: 2ex;"><a href="javascript:history.go(-1)">Back</a></div>
But nothing has timed out because when I hit Post, it works fine.
Jits, maybe you can figure this out.