This was mentioned in another post, which I can't find, but wanted to give folks a heads up. The issue here and like a lot of other feeds that are failing is due to the new modules validation of feeds prior to displaying them. The RSS v2.0 spec is strictly enforced, and that spec calls for a pubDate element to be in an RFC822 format.
Many folks, developers included, don't really give a hoot about what the RSS spec or an RFC822 spec is about, but the specs were designed to give folks confidence in the data structure being delivered, and make it something 'not' to have to worry about. Ok, utopian view, but that's the reason for them. Unfortunately, everyone seems to code with their own idea of what should be distributed, and the RSS v2.0 spec or any other for that matter, is not followed.
Now, there are many other examples of feeds that are not using RFC822 formatted dates, and that is causing a lot of feeds to fail. I know that Peter is looking into the issue, and I'm going over the code this week, too. My first impression is that the new module is being too strict, given the lack of public newfeed sources following the RSS v2.0 spec. However, the new module is attempting to allow it to be used as a news agregattor, and that is a very difficult task, as it is also, trying to automate the transformation of several different feed formats into RSS v2.0. Trouble is Atom and RSS v1.0 (RDF) type feeds don't really have a pubDate element.
I think there is some workaround possible, and I'm looking into the issue and will discuss it with Peter, when I get more familiar with the source. Meantime, if you are getting this error with a feed, take a look at the news feed source code to see if your pubDate element in the feeds is in RFC822 format.
Usually, it's a date in this format: Wed, 10 Sep 2008 15:03:53 GMT - where the day of the week and secconds is optional.
Now, this is kind of embarrassing for a DNN core module to not follow the standard, but the Forums module is not following the RSS v2.0 spec either. If you take a look at the source rss newsfeed emitted from the module you'll see this in the pubDate element:
<pubDate>2007-06-09T08:00:08Z</pubDate>
You will get the error message:
The 'pubDate' element is invalid - The value '2008-09-10T11:07:50Z' is invalid according to its datatype 'tRfc822formatDate' - The Pattern constraint failed.