I think this is a bug, since nested lists are [url=http://www.w3.org/TR/2003/WD-xhtml2-20030506/mod-list.html]allowed in xhtml[/url]. I tried to post an outline like this:
<ol>
<li>number one</li>
<li>numer two</li>
<li>number thee</li>
<li>number four
<ol>
<li>four-a</li>
<li>four-b</li>
<li>lfour-c</li>
</ol>
<li>number five</li>
</ol>
and I got this error:
Invalid post, please correct these errors:
* Tag li is not allowed within tag li
I think the problem is that you did not close your <li> after the nested list, so it appears you are trying to put a <li> inside a <li>. Try this: