Following the installation of SharePoint 2010 SP2 (KB2687453) I found that the RSS viewer web part had stopped working; the web part continually showed the loading image.

After some research I discovered that the issue was introduced in SharePoint 2010 February 12, 2013 cumulative update (KB2767793). Some suggested fixes are listed on the SharePoint forums.
The first option is to add a Content Editor Web Part to any page with the RSS viewer web part and paste the JavaScript below into the web part in HTML view. Although this works it’s not a realistic work around if you have many pages with the RSS viewer web part.
<script type=”text/javascript”>
function CustomUpdateFormDigest()
{
if(window._spPageContextInfo != null)
{
var $v_2 = window._spPageContextInfo;
var $v_3 = $v_2.webServerRelativeUrl;
var $v_4 = window._spFormDigestRefreshInterval;
UpdateFormDigest($v_3, $v_4);
}
}
CustomUpdateFormDigest();
</script>
The second option is to add the above script to the SharePoint master page, but I couldn’t get this to work.
The third option is to turn off web page security validation for the web application from Central Administration -> Manage web applications. Highlight the affected web application and select General Settings from the ribbon.

Turning off web page security validation worked, but I was then unable to create any new sites or lists because I received the error “An unhandled exception occured in the Silverlight application SharePoint 2010.
I have just finished testing the August 13, 2013 cumulative update for SharePoint 2010 (KB2817570) and it appears to fix the RSS viewer issue without any side affects.
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