Hi Dan,
That link should be in the meta data inside the head element if you view the source of the page containing your blog. If you google for "rss feed autodiscovery" you can learn about its purpose.
The url itself should work so maybe that is what it is complaining about if it doesn't, but other than that it should not affect seo.
Current version of mojoportal uses a different format for the feed url but older versions used a format like what you posted, the friendly url was created automatically upon making the first blog post in older versions so the url could be on the page but not work if there are no posts. In newer versions of mojoportal we use a feed url in the format:
/Blog/RSS.aspx?p=18~30~-1&r=ce2ea88e-96b7-4467-897c-ff873b201e1a
which does correspond to a real url.
Hope that helps,
Joe