RSS loading problems can be caused by a variety of factors. This document will attempt to explain the variety of issues, with workarounds where available.
First, make sure that the RSS feed you are loading is a "Media RSS" feed. If you load the XML file in Firefox, and view the source, you should see something like this at the top:
<rss version="2.0" xmlns:media="http://search.yahoo.com/mrss/">
This type of RSS feed was created by Yahoo! in 2004 for distributing media (like photos and videos), is widely adopted, and thus is the only type of RSS feed SlideShowPro for Flash can load. If you don't see this in your RSS feed, chances are it won't load. Check with the third party to see if they publish RSS links in alternate formats.
Just like traditional XML, RSS is subject to the same security limitations imposed by the Flash Player's security system. In other words, an RSS feed will only load if the third party site publishing the document grants SWFs embedded at outside domains to load their content. It may seem strange to publish a public RSS feed that can be read by anything other than the Flash Player, but some third parties don't. Those that do will have a file named crossdomain.xml in the root of their domain that includes RSS/XML loading permissions. You can check this by looking at the domain where your RSS feed is coming from and attaching "crossdomain.xml" onto it, like so:
http://api.flickr.com/crossdomain.xml
If the site has a wildcard ("*") it means that a SWF embedded at any domain can load its RSS feed. If not, and they include specific domains in their crossdomain.xml (and you're not on that list) the feed will not load. You should contact the third party site about this if necessary.
Here are a few RSS related tips from popular third party sites we've come across over time. If you have one you'd like so share, let us know!
Flickr publishes both Media RSS and Atom feeds. Atom feeds are not supported, so be sure to check the RSS source for the Media RSS header (explained above) to ensure you have the right file.
Also, make sure when loading Flickr's RSS feeds that the following is at the end of the RSS url, if not already:
&format=rss_200
SmugMug publishes Media RSS feeds, but (last time we checked) their published feeds can't be loaded by SWFs at remote domains. You can however load their feeds by adding a special "Sandboxed" parameter onto any feed URL, like so:
http://api.smugmug.com/hack/feed.mg?Type=gallery&Data=6163403_wRRvp&format=rss200&Size=Large&Sandboxed=1
By assigning "&Sandboxed=1", the RSS feed will load content from a domain that permits SWFs to load its data.
Picasa permits RSS parsing by Flash applications through an alternate domain. First, take copy the RSS feed URL from Picasa, which should look something like this:
http://picasaweb.google.com/data/feed/base/user/username/albumid/5306107343223089553?alt=rss&kind=photo&hl=en_US
Change "picasaweb.google.com" to "photos.googleapis.com", like so:
http://photos.googleapis.com/data/feed/base/user/username/albumid/5306107343223089553?alt=rss&kind=photo&hl=en_US
Next, create a new timeline layer in your FLA, click inside the empty keyframe, open the "Actions" panel, and enter this:
Security.loadPolicyFile("http://photos.googleapis.com/data/crossdomain.xml");
Publish a SWF, upload it to your web site, and view it in a HTML document. The content from Picasa should then load.