A missing text attribute in any outline element is an error.NetVibes' <outline> elements look something like this:
<outline title="Netvibes Blog" type="rss" xmlUrl="http://feeds.feedburner.com/NetvibesDevBlog" htmlUrl="http://blog.netvibes.com"/>
It's very easy to fix -- just add a new "text" attribute with the contents of the existing "title" attribute. It trips up some other OPML importers, though.
[Edit: I wrote a little python script to fix this problem specifically: https://github.com/mjkelly/experiments/blob/master/opml-fix-text-attr.py]