Ok, my bad.  I left out an importand characteristic of the category value.  You need to specify the height in px for the info to display.  If you look at the fallback opml, you will see they always specify 3000px to allow for probably more than you need.  Anyhow, you will get the URL is not defined message if something is amiss in the opml text.  There is a limit on how many chars it will translate (don't know what it is exactly), which is why you should use an opml text file if you are doing many tabs, sections, or categories. 

Bottom line, try cutting and pasting your existing opml text into a text file for saving.  Then, copy and paste this example in your opml textbox.

<outline text="WizzoDawg" type="none" category="Tab">
 <outline text="News" type="none" category="Section">
<outline text="Youth Development" type="rss" category="Category/@@3000px" xmlUrl="http://news.google.com/news?hl=en&amp;tab=wn&amp;ned=us&amp;q=youth+development&amp;as_drrb=q&amp;as_qdr=w&amp;as_mind=27&amp;as_minm=12&amp;as_maxd=3&amp;as_maxm=1&amp;nolr=1&amp;output=rss" />
 </outline>
</outline>
 

What we are doing is just testing the one URL.  Work with this example, and let me know what you get.

I'm am using it without issue, which is why I know it's working.  Also, note the /@@3000px I've added to the category value.  If you don't have any value, the value is zero, and nothing will display.  As I said, I fat fingered it, in the earlier example, this time I copied the opml text exactly as I am using it.

If you opt for using a custom opml text file, there are some  formatting issues, so check back with me.

Cheers