Can't add RSS feed

When I paste the following feed into the Add Site dialog, it tells me that there was a problem and to “try a different URL”.

The W3C feed validator flags a few issues (e.g., with non-RFC-822 dates): is this the problem?

PS: I will add that the error message telling people to “try a different URL” is both unhelpful and (unintentionally) somewhat insulting. I didn’t buy your product to read random things: I need to keep up on specific technical topics.

A less-bad error message might be “make sure your URL contains a valid feed.” A good error message would explain exactly why I can’t use the feed I’m specifically asking for. E.g.,
* ATOM/RSS link not found (for HTML content type),
* URL not responding,
* invalid feed structure (for ATOM/RSS content type),
* unknown server error,
* etc

Without an actionable error message, the only real options available to a user are to file a ticket or give up on using your product for the feed(s) he or she needs. (I’m generally quite happy with the product, so here I am filing a ticket.)