Doing a bit more poking around, it looks like the problem is there's a % in the URL in the News Listing links--the link from the front page is fine and does not have the %.

<r> The link for the D-Day Sale news item returns a 400 error for an invalid URL when accessed directly (that is, not through the link from email, which has other tracking information in it.<br/>
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I can't link the URL directly, but it happens if you click on the news item from the news ...