For anyone who has started to whittle back the OOTB master pages in MOSS 2007, and wondered why their webpart pages break – the tools panel appears below the main content – then check you still have the
<PlaceHolder id=”MSO_ContentDiv” runat=”server”>
…
</PlaceHolder>
This bespoke tag applies a </table> with no opening <table> when you click to ‘Edit’ any webpart. Without this little baby, your webpart pages will not render as expected.
See http://blogs.msdn.com/ecm/archive/2006/09/21/764759.aspx for a quick mention on issue.